diff options
Diffstat (limited to 'drivers/lguest')
| -rw-r--r-- | drivers/lguest/Kconfig | 30 | ||||
| -rw-r--r-- | drivers/lguest/Makefile | 19 | ||||
| -rw-r--r-- | drivers/lguest/README | 47 | ||||
| -rw-r--r-- | drivers/lguest/core.c | 776 | ||||
| -rw-r--r-- | drivers/lguest/hypercalls.c | 300 | ||||
| -rw-r--r-- | drivers/lguest/interrupts_and_traps.c | 446 | ||||
| -rw-r--r-- | drivers/lguest/io.c | 626 | ||||
| -rw-r--r-- | drivers/lguest/lg.h | 300 | ||||
| -rw-r--r-- | drivers/lguest/lguest.c | 1102 | ||||
| -rw-r--r-- | drivers/lguest/lguest_asm.S | 93 | ||||
| -rw-r--r-- | drivers/lguest/lguest_bus.c | 218 | ||||
| -rw-r--r-- | drivers/lguest/lguest_user.c | 382 | ||||
| -rw-r--r-- | drivers/lguest/page_tables.c | 680 | ||||
| -rw-r--r-- | drivers/lguest/segments.c | 177 | ||||
| -rw-r--r-- | drivers/lguest/switcher.S | 350 |
15 files changed, 5546 insertions, 0 deletions
diff --git a/drivers/lguest/Kconfig b/drivers/lguest/Kconfig new file mode 100644 index 00000000000..41e2250613a --- /dev/null +++ b/drivers/lguest/Kconfig @@ -0,0 +1,30 @@ +config LGUEST + tristate "Linux hypervisor example code" + depends on X86 && PARAVIRT && EXPERIMENTAL && !X86_PAE && FUTEX + select LGUEST_GUEST + select HVC_DRIVER + ---help--- + This is a very simple module which allows you to run + multiple instances of the same Linux kernel, using the + "lguest" command found in the Documentation/lguest directory. + Note that "lguest" is pronounced to rhyme with "fell quest", + not "rustyvisor". See Documentation/lguest/lguest.txt. + + If unsure, say N. If curious, say M. If masochistic, say Y. + +config LGUEST_GUEST + bool + help + The guest needs code built-in, even if the host has lguest + support as a module. The drivers are tiny, so we build them + in too. + +config LGUEST_NET + tristate + default y + depends on LGUEST_GUEST && NET + +config LGUEST_BLOCK + tristate + default y + depends on LGUEST_GUEST && BLOCK diff --git a/drivers/lguest/Makefile b/drivers/lguest/Makefile new file mode 100644 index 00000000000..e5047471c33 --- /dev/null +++ b/drivers/lguest/Makefile @@ -0,0 +1,19 @@ +# Guest requires the paravirt_ops replacement and the bus driver. +obj-$(CONFIG_LGUEST_GUEST) += lguest.o lguest_asm.o lguest_bus.o + +# Host requires the other files, which can be a module. +obj-$(CONFIG_LGUEST) += lg.o +lg-y := core.o hypercalls.o page_tables.o interrupts_and_traps.o \ + segments.o io.o lguest_user.o switcher.o + +Preparation Preparation!: PREFIX=P +Guest: PREFIX=G +Drivers: PREFIX=D +Launcher: PREFIX=L +Host: PREFIX=H +Switcher: PREFIX=S +Mastery: PREFIX=M +Beer: + @for f in Preparation Guest Drivers Launcher Host Switcher Mastery; do echo "{==- $$f -==}"; make -s $$f; done; echo "{==-==}" +Preparation Preparation! Guest Drivers Launcher Host Switcher Mastery: + @sh ../../Documentation/lguest/extract $(PREFIX) `find ../../* -name '*.[chS]' -wholename '*lguest*'` diff --git a/drivers/lguest/README b/drivers/lguest/README new file mode 100644 index 00000000000..b7db39a64c6 --- /dev/null +++ b/drivers/lguest/README @@ -0,0 +1,47 @@ +Welcome, friend reader, to lguest. + +Lguest is an adventure, with you, the reader, as Hero. I can't think of many +5000-line projects which offer both such capability and glimpses of future +potential; it is an exciting time to be delving into the source! + +But be warned; this is an arduous journey of several hours or more! And as we +know, all true Heroes are driven by a Noble Goal. Thus I offer a Beer (or +equivalent) to anyone I meet who has completed this documentation. + +So get comfortable and keep your wits about you (both quick and humorous). +Along your way to the Noble Goal, you will also gain masterly insight into +lguest, and hypervisors and x86 virtualization in general. + +Our Quest is in seven parts: (best read with C highlighting turned on) + +I) Preparation + - In which our potential hero is flown quickly over the landscape for a + taste of its scope. Suitable for the armchair coders and other such + persons of faint constitution. + +II) Guest + - Where we encounter the first tantalising wisps of code, and come to + understand the details of the life of a Guest kernel. + +III) Drivers + - Whereby the Guest finds its voice and become useful, and our + understanding of the Guest is completed. + +IV) Launcher + - Where we trace back to the creation of the Guest, and thus begin our + understanding of the Host. + +V) Host + - Where we master the Host code, through a long and tortuous journey. + Indeed, it is here that our hero is tested in the Bit of Despair. + +VI) Switcher + - Where our understanding of the intertwined nature of Guests and Hosts + is completed. + +VII) Mastery + - Where our fully fledged hero grapples with the Great Question: + "What next?" + +make Preparation! +Rusty Russell. diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c new file mode 100644 index 00000000000..4a315f08a56 --- /dev/null +++ b/drivers/lguest/core.c @@ -0,0 +1,776 @@ +/*P:400 This contains run_guest() which actually calls into the Host<->Guest + * Switcher and analyzes the return, such as determining if the Guest wants the + * Host to do something. This file also contains useful helper routines, and a + * couple of non-obvious setup and teardown pieces which were implemented after + * days of debugging pain. :*/ +#include <linux/module.h> +#include <linux/stringify.h> +#include <linux/stddef.h> +#include <linux/io.h> +#include <linux/mm.h> +#include <linux/vmalloc.h> +#include <linux/cpu.h> +#include <linux/freezer.h> +#include <asm/paravirt.h> +#include <asm/desc.h> +#include <asm/pgtable.h> +#include <asm/uaccess.h> +#include <asm/poll.h> +#include <asm/highmem.h> +#include <asm/asm-offsets.h> +#include <asm/i387.h> +#include "lg.h" + +/* Found in switcher.S */ +extern char start_switcher_text[], end_switcher_text[], switch_to_guest[]; +extern unsigned long default_idt_entries[]; + +/* Every guest maps the core switcher code. */ +#define SHARED_SWITCHER_PAGES \ + DIV_ROUND_UP(end_switcher_text - start_switcher_text, PAGE_SIZE) +/* Pages for switcher itself, then two pages per cpu */ +#define TOTAL_SWITCHER_PAGES (SHARED_SWITCHER_PAGES + 2 * NR_CPUS) + +/* We map at -4M for ease of mapping into the guest (one PTE page). */ +#define SWITCHER_ADDR 0xFFC00000 + +static struct vm_struct *switcher_vma; +static struct page **switcher_page; + +static int cpu_had_pge; +static struct { + unsigned long offset; + unsigned short segment; +} lguest_entry; + +/* This One Big lock protects all inter-guest data structures. */ +DEFINE_MUTEX(lguest_lock); +static DEFINE_PER_CPU(struct lguest *, last_guest); + +/* FIXME: Make dynamic. */ +#define MAX_LGUEST_GUESTS 16 +struct lguest lguests[MAX_LGUEST_GUESTS]; + +/* Offset from where switcher.S was compiled to where we've copied it */ +static unsigned long switcher_offset(void) +{ + return SWITCHER_ADDR - (unsigned long)start_switcher_text; +} + +/* This cpu's struct lguest_pages. */ +static struct lguest_pages *lguest_pages(unsigned int cpu) +{ + return &(((struct lguest_pages *) + (SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]); +} + +/*H:010 We need to set up the Switcher at a high virtual address. Remember the + * Switcher is a few hundred bytes of assembler code which actually changes the + * CPU to run the Guest, and then changes back to the Host when a trap or + * interrupt happens. + * + * The Switcher code must be at the same virtual address in the Guest as the + * Host since it will be running as the switchover occurs. + * + * Trying to map memory at a particular address is an unusual thing to do, so + * it's not a simple one-liner. We also set up the per-cpu parts of the + * Switcher here. + */ +static __init int map_switcher(void) +{ + int i, err; + struct page **pagep; + + /* + * Map the Switcher in to high memory. + * + * It turns out that if we choose the address 0xFFC00000 (4MB under the + * top virtual address), it makes setting up the page tables really + * easy. + */ + + /* We allocate an array of "struct page"s. map_vm_area() wants the + * pages in this form, rather than just an array of pointers. */ + switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES, + GFP_KERNEL); + if (!switcher_page) { + err = -ENOMEM; + goto out; + } + + /* Now we actually allocate the pages. The Guest will see these pages, + * so we make sure they're zeroed. */ + for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) { + unsigned long addr = get_zeroed_page(GFP_KERNEL); + if (!addr) { + err = -ENOMEM; + goto free_some_pages; + } + switcher_page[i] = virt_to_page(addr); + } + + /* Now we reserve the "virtual memory area" we want: 0xFFC00000 + * (SWITCHER_ADDR). We might not get it in theory, but in practice + * it's worked so far. */ + switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE, + VM_ALLOC, SWITCHER_ADDR, VMALLOC_END); + if (!switcher_vma) { + err = -ENOMEM; + printk("lguest: could not map switcher pages high\n"); + goto free_pages; + } + + /* This code actually sets up the pages we've allocated to appear at + * SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the + * kind of pages we're mapping (kernel pages), and a pointer to our + * array of struct pages. It increments that pointer, but we don't + * care. */ + pagep = switcher_page; + err = map_vm_area(switcher_vma, PAGE_KERNEL, &pagep); + if (err) { + printk("lguest: map_vm_area failed: %i\n", err); + goto free_vma; + } + + /* Now the switcher is mapped at the right address, we can't fail! + * Copy in the compiled-in Switcher code (from switcher.S). */ + memcpy(switcher_vma->addr, start_switcher_text, + end_switcher_text - start_switcher_text); + + /* Most of the switcher.S doesn't care that it's been moved; on Intel, + * jumps are relative, and it doesn't access any references to external + * code or data. + * + * The only exception is the interrupt handlers in switcher.S: their + * addresses are placed in a table (default_idt_entries), so we need to + * update the table with the new addresses. switcher_offset() is a + * convenience function which returns the distance between the builtin + * switcher code and the high-mapped copy we just made. */ + for (i = 0; i < IDT_ENTRIES; i++) + default_idt_entries[i] += switcher_offset(); + + /* + * Set up the Switcher's per-cpu areas. + * + * Each CPU gets two pages of its own within the high-mapped region + * (aka. "struct lguest_pages"). Much of this can be initialized now, + * but some depends on what Guest we are running (which is set up in + * copy_in_guest_info()). + */ + for_each_possible_cpu(i) { + /* lguest_pages() returns this CPU's two pages. */ + struct lguest_pages *pages = lguest_pages(i); + /* This is a convenience pointer to make the code fit one + * statement to a line. */ + struct lguest_ro_state *state = &pages->state; + + /* The Global Descriptor Table: the Host has a different one + * for each CPU. We keep a descriptor for the GDT which says + * where it is and how big it is (the size is actually the last + * byte, not the size, hence the "-1"). */ + state->host_gdt_desc.size = GDT_SIZE-1; + state->host_gdt_desc.address = (long)get_cpu_gdt_table(i); + + /* All CPUs on the Host use the same Interrupt Descriptor + * Table, so we just use store_idt(), which gets this CPU's IDT + * descriptor. */ + store_idt(&state->host_idt_desc); + + /* The descriptors for the Guest's GDT and IDT can be filled + * out now, too. We copy the GDT & IDT into ->guest_gdt and + * ->guest_idt before actually running the Guest. */ + state->guest_idt_desc.size = sizeof(state->guest_idt)-1; + state->guest_idt_desc.address = (long)&state->guest_idt; + state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1; + state->guest_gdt_desc.address = (long)&state->guest_gdt; + + /* We know where we want the stack to be when the Guest enters + * the switcher: in pages->regs. The stack grows upwards, so + * we start it at the end of that structure. */ + state->guest_tss.esp0 = (long)(&pages->regs + 1); + /* And this is the GDT entry to use for the stack: we keep a + * couple of special LGUEST entries. */ + state->guest_tss.ss0 = LGUEST_DS; + + /* x86 can have a finegrained bitmap which indicates what I/O + * ports the process can use. We set it to the end of our + * structure, meaning "none". */ + state->guest_tss.io_bitmap_base = sizeof(state->guest_tss); + + /* Some GDT entries are the same across all Guests, so we can + * set them up now. */ + setup_default_gdt_entries(state); + /* Most IDT entries are the same for all Guests, too.*/ + setup_default_idt_entries(state, default_idt_entries); + + /* The Host needs to be able to use the LGUEST segments on this + * CPU, too, so put them in the Host GDT. */ + get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT; + get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT; + } + + /* In the Switcher, we want the %cs segment register to use the + * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so + * it will be undisturbed when we switch. To change %cs and jump we + * need this structure to feed to Intel's "lcall" instruction. */ + lguest_entry.offset = (long)switch_to_guest + switcher_offset(); + lguest_entry.segment = LGUEST_CS; + + printk(KERN_INFO "lguest: mapped switcher at %p\n", + switcher_vma->addr); + /* And we succeeded... */ + return 0; + +free_vma: + vunmap(switcher_vma->addr); +free_pages: + i = TOTAL_SWITCHER_PAGES; +free_some_pages: + for (--i; i >= 0; i--) + __free_pages(switcher_page[i], 0); + kfree(switcher_page); +out: + return err; +} +/*:*/ + +/* Cleaning up the mapping when the module is unloaded is almost... + * too easy. */ +static void unmap_switcher(void) +{ + unsigned int i; + + /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */ + vunmap(switcher_vma->addr); + /* Now we just need to free the pages we copied the switcher into */ + for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) + __free_pages(switcher_page[i], 0); +} + +/*H:130 Our Guest is usually so well behaved; it never tries to do things it + * isn't allowed to. Unfortunately, "struct paravirt_ops" isn't quite + * complete, because it doesn't contain replacements for the Intel I/O + * instructions. As a result, the Guest sometimes fumbles across one during + * the boot process as it probes for various things which are usually attached + * to a PC. + * + * When the Guest uses one of these instructions, we get trap #13 (General + * Protection Fault) and come here. We see if it's one of those troublesome + * instructions and skip over it. We return true if we did. */ +static int emulate_insn(struct lguest *lg) +{ + u8 insn; + unsigned int insnlen = 0, in = 0, shift = 0; + /* The eip contains the *virtual* address of the Guest's instruction: + * guest_pa just subtracts the Guest's page_offset. */ + unsigned long physaddr = guest_pa(lg, lg->regs->eip); + + /* The guest_pa() function only works for Guest kernel addresses, but + * that's all we're trying to do anyway. */ + if (lg->regs->eip < lg->page_offset) + return 0; + + /* Decoding x86 instructions is icky. */ + lgread(lg, &insn, physaddr, 1); + + /* 0x66 is an "operand prefix". It means it's using the upper 16 bits + of the eax register. */ + if (insn == 0x66) { + shift = 16; + /* The instruction is 1 byte so far, read the next byte. */ + insnlen = 1; + lgread(lg, &insn, physaddr + insnlen, 1); + } + + /* We can ignore the lower bit for the moment and decode the 4 opcodes + * we need to emulate. */ + switch (insn & 0xFE) { + case 0xE4: /* in <next byte>,%al */ + insnlen += 2; + in = 1; + break; + case 0xEC: /* in (%dx),%al */ + insnlen += 1; + in = 1; + break; + case 0xE6: /* out %al,<next byte> */ + insnlen += 2; + break; + case 0xEE: /* out %al,(%dx) */ + insnlen += 1; + break; + default: + /* OK, we don't know what this is, can't emulate. */ + return 0; + } + + /* If it was an "IN" instruction, they expect the result to be read + * into %eax, so we change %eax. We always return all-ones, which + * traditionally means "there's nothing there". */ + if (in) { + /* Lower bit tells is whether it's a 16 or 32 bit access */ + if (insn & 0x1) + lg->regs->eax = 0xFFFFFFFF; + else + lg->regs->eax |= (0xFFFF << shift); + } + /* Finally, we've "done" the instruction, so move past it. */ + lg->regs->eip += insnlen; + /* Success! */ + return 1; +} +/*:*/ + +/*L:305 + * Dealing With Guest Memory. + * + * When the Guest gives us (what it thinks is) a physical address, we can use + * the normal copy_from_user() & copy_to_user() on that address: remember, + * Guest physical == Launcher virtual. + * + * But we can't trust the Guest: it might be trying to access the Launcher + * code. We have to check that the range is below the pfn_limit the Launcher + * gave us. We have to make sure that addr + len doesn't give us a false + * positive by overflowing, too. */ +int lguest_address_ok(const struct lguest *lg, + unsigned long addr, unsigned long len) +{ + return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr); +} + +/* This is a convenient routine to get a 32-bit value from the Guest (a very + * common operation). Here we can see how useful the kill_lguest() routine we + * met in the Launcher can be: we return a random value (0) instead of needing + * to return an error. */ +u32 lgread_u32(struct lguest *lg, unsigned long addr) +{ + u32 val = 0; + + /* Don't let them access lguest binary. */ + if (!lguest_address_ok(lg, addr, sizeof(val)) + || get_user(val, (u32 __user *)addr) != 0) + kill_guest(lg, "bad read address %#lx", addr); + return val; +} + +/* Same thing for writing a value. */ +void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val) +{ + if (!lguest_address_ok(lg, addr, sizeof(val)) + || put_user(val, (u32 __user *)addr) != 0) + kill_guest(lg, "bad write address %#lx", addr); +} + +/* This routine is more generic, and copies a range of Guest bytes into a + * buffer. If the copy_from_user() fails, we fill the buffer with zeroes, so + * the caller doesn't end up using uninitialized kernel memory. */ +void lgread(struct lguest *lg, void *b, unsigned long addr, unsigned bytes) +{ + if (!lguest_address_ok(lg, addr, bytes) + || copy_from_user(b, (void __user *)addr, bytes) != 0) { + /* copy_from_user should do this, but as we rely on it... */ + memset(b, 0, bytes); + kill_guest(lg, "bad read address %#lx len %u", addr, bytes); + } +} + +/* Similarly, our generic routine to copy into a range of Guest bytes. */ +void lgwrite(struct lguest *lg, unsigned long addr, const void *b, + unsigned bytes) +{ + if (!lguest_address_ok(lg, addr, bytes) + || copy_to_user((void __user *)addr, b, bytes) != 0) + kill_guest(lg, "bad write address %#lx len %u", addr, bytes); +} +/* (end of memory access helper routines) :*/ + +static void set_ts(void) +{ + u32 cr0; + + cr0 = read_cr0(); + if (!(cr0 & 8)) + write_cr0(cr0|8); +} + +/*S:010 + * We are getting close to the Switcher. + * + * Remember that each CPU has two pages which are visible to the Guest when it + * runs on that CPU. This has to contain the state for that Guest: we copy the + * state in just before we run the Guest. + * + * Each Guest has "changed" flags which indicate what has changed in the Guest + * since it last ran. We saw this set in interrupts_and_traps.c and + * segments.c. + */ +static void copy_in_guest_info(struct lguest *lg, struct lguest_pages *pages) +{ + /* Copying all this data can be quite expensive. We usually run the + * same Guest we ran last time (and that Guest hasn't run anywhere else + * meanwhile). If that's not the case, we pretend everything in the + * Guest has changed. */ + if (__get_cpu_var(last_guest) != lg || lg->last_pages != pages) { + __get_cpu_var(last_guest) = lg; + lg->last_pages = pages; + lg->changed = CHANGED_ALL; + } + + /* These copies are pretty cheap, so we do them unconditionally: */ + /* Save the current Host top-level page directory. */ + pages->state.host_cr3 = __pa(current->mm->pgd); + /* Set up the Guest's page tables to see this CPU's pages (and no + * other CPU's pages). */ + map_switcher_in_guest(lg, pages); + /* Set up the two "TSS" members which tell the CPU what stack to use + * for traps which do directly into the Guest (ie. traps at privilege + * level 1). */ + pages->state.guest_tss.esp1 = lg->esp1; + pages->state.guest_tss.ss1 = lg->ss1; + + /* Copy direct-to-Guest trap entries. */ + if (lg->changed & CHANGED_IDT) + copy_traps(lg, pages->state.guest_idt, default_idt_entries); + + /* Copy all GDT entries which the Guest can change. */ + if (lg->changed & CHANGED_GDT) + copy_gdt(lg, pages->state.guest_gdt); + /* If only the TLS entries have changed, copy them. */ + else if (lg->changed & CHANGED_GDT_TLS) + copy_gdt_tls(lg, pages->state.guest_gdt); + + /* Mark the Guest as unchanged for next time. */ + lg->changed = 0; +} + +/* Finally: the code to actually call into the Switcher to run the Guest. */ +static void run_guest_once(struct lguest *lg, struct lguest_pages *pages) +{ + /* This is a dummy value we need for GCC's sake. */ + unsigned int clobber; + + /* Copy the guest-specific information into this CPU's "struct + * lguest_pages". */ + copy_in_guest_info(lg, pages); + + /* Set the trap number to 256 (impossible value). If we fault while + * switching to the Guest (bad segment registers or bug), this will + * cause us to abort the Guest. */ + lg->regs->trapnum = 256; + + /* Now: we push the "eflags" register on the stack, then do an "lcall". + * This is how we change from using the kernel code segment to using + * the dedicated lguest code segment, as well as jumping into the + * Switcher. + * + * The lcall also pushes the old code segment (KERNEL_CS) onto the + * stack, then the address of this call. This stack layout happens to + * exactly match the stack of an interrupt... */ + asm volatile("pushf; lcall *lguest_entry" + /* This is how we tell GCC that %eax ("a") and %ebx ("b") + * are changed by this routine. The "=" means output. */ + : "=a"(clobber), "=b"(clobber) + /* %eax contains the pages pointer. ("0" refers to the + * 0-th argument above, ie "a"). %ebx contains the + * physical address of the Guest's top-level page + * directory. */ + : "0"(pages), "1"(__pa(lg->pgdirs[lg->pgdidx].pgdir)) + /* We tell gcc that all these registers could change, + * which means we don't have to save and restore them in + * the Switcher. */ + : "memory", "%edx", "%ecx", "%edi", "%esi"); +} +/*:*/ + +/*H:030 Let's jump straight to the the main loop which runs the Guest. + * Remember, this is called by the Launcher reading /dev/lguest, and we keep + * going around and around until something interesting happens. */ +int run_guest(struct lguest *lg, unsigned long __user *user) +{ + /* We stop running once the Guest is dead. */ + while (!lg->dead) { + /* We need to initialize this, otherwise gcc complains. It's + * not (yet) clever enough to see that it's initialized when we + * need it. */ + unsigned int cr2 = 0; /* Damn gcc */ + + /* First we run any hypercalls the Guest wants done: either in + * the hypercall ring in "struct lguest_data", or directly by + * using int 31 (LGUEST_TRAP_ENTRY). */ + do_hypercalls(lg); + /* It's possible the Guest did a SEND_DMA hypercall to the + * Launcher, in which case we return from the read() now. */ + if (lg->dma_is_pending) { + if (put_user(lg->pending_dma, user) || + put_user(lg->pending_key, user+1)) + return -EFAULT; + return sizeof(unsigned long)*2; + } + + /* Check for signals */ + if (signal_pending(current)) + return -ERESTARTSYS; + + /* If Waker set break_out, return to Launcher. */ + if (lg->break_out) + return -EAGAIN; + + /* Check if there are any interrupts which can be delivered + * now: if so, this sets up the hander to be executed when we + * next run the Guest. */ + maybe_do_interrupt(lg); + + /* All long-lived kernel loops need to check with this horrible + * thing called the freezer. If the Host is trying to suspend, + * it stops us. */ + try_to_freeze(); + + /* Just make absolutely sure the Guest is still alive. One of + * those hypercalls could have been fatal, for example. */ + if (lg->dead) + break; + + /* If the Guest asked to be stopped, we sleep. The Guest's + * clock timer or LHCALL_BREAK from the Waker will wake us. */ + if (lg->halted) { + set_current_state(TASK_INTERRUPTIBLE); + schedule(); + continue; + } + + /* OK, now we're ready to jump into the Guest. First we put up + * the "Do Not Disturb" sign: */ + local_irq_disable(); + + /* Remember the awfully-named TS bit? If the Guest has asked + * to set it we set it now, so we can trap and pass that trap + * to the Guest if it uses the FPU. */ + if (lg->ts) + set_ts(); + + /* SYSENTER is an optimized way of doing system calls. We + * can't allow it because it always jumps to privilege level 0. + * A normal Guest won't try it because we don't advertise it in + * CPUID, but a malicious Guest (or malicious Guest userspace + * program) could, so we tell the CPU to disable it before + * running the Guest. */ + if (boot_cpu_has(X86_FEATURE_SEP)) + wrmsr(MSR_IA32_SYSENTER_CS, 0, 0); + + /* Now we actually run the Guest. It will pop back out when + * something interesting happens, and we can examine its + * registers to see what it was doing. */ + run_guest_once(lg, lguest_pages(raw_smp_processor_id())); + + /* The "regs" pointer contains two extra entries which are not + * really registers: a trap number which says what interrupt or + * trap made the switcher code come back, and an error code + * which some traps set. */ + + /* If the Guest page faulted, then the cr2 register will tell + * us the bad virtual address. We have to grab this now, + * because once we re-enable interrupts an interrupt could + * fault and thus overwrite cr2, or we could even move off to a + * different CPU. */ + if (lg->regs->trapnum == 14) + cr2 = read_cr2(); + /* Similarly, if we took a trap because the Guest used the FPU, + * we have to restore the FPU it expects to see. */ + else if (lg->regs->trapnum == 7) + math_state_restore(); + + /* Restore SYSENTER if it's supposed to be on. */ + if (boot_cpu_has(X86_FEATURE_SEP)) + wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0); + + /* Now we're ready to be interrupted or moved to other CPUs */ + local_irq_enable(); + + /* OK, so what happened? */ + switch (lg->regs->trapnum) { + case 13: /* We've intercepted a GPF. */ + /* Check if this was one of those annoying IN or OUT + * instructions which we need to emulate. If so, we + * just go back into the Guest after we've done it. */ + if (lg->regs->errcode == 0) { + if (emulate_insn(lg)) + continue; + } + break; + case 14: /* We've intercepted a page fault. */ + /* The Guest accessed a virtual address that wasn't + * mapped. This happens a lot: we don't actually set + * up most of the page tables for the Guest at all when + * we start: as it runs it asks for more and more, and + * we set them up as required. In this case, we don't + * even tell the Guest that the fault happened. + * + * The errcode tells whether this was a read or a + * write, and whether kernel or userspace code. */ + if (demand_page(lg, cr2, lg->regs->errcode)) + continue; + + /* OK, it's really not there (or not OK): the Guest + * needs to know. We write out the cr2 value so it + * knows where the fault occurred. + * + * Note that if the Guest were really messed up, this + * could happen before it's done the INITIALIZE + * hypercall, so lg->lguest_data will be NULL, so + * &lg->lguest_data->cr2 will be address 8. Writing + * into that address won't hurt the Host at all, + * though. */ + if (put_user(cr2, &lg->lguest_data->cr2)) + kill_guest(lg, "Writing cr2"); + break; + case 7: /* We've intercepted a Device Not Available fault. */ + /* If the Guest doesn't want to know, we already + * restored the Floating Point Unit, so we just + * continue without telling it. */ + if (!lg->ts) + continue; + break; + case 32 ... 255: + /* These values mean a real interrupt occurred, in + * which case the Host handler has already been run. + * We just do a friendly check if another process + * should now be run, then fall through to loop + * around: */ + cond_resched(); + case LGUEST_TRAP_ENTRY: /* Handled at top of loop */ + continue; + } + + /* If we get here, it's a trap the Guest wants to know + * about. */ + if (deliver_trap(lg, lg->regs->trapnum)) + continue; + + /* If the Guest doesn't have a handler (either it hasn't + * registered any yet, or it's one of the faults we don't let + * it handle), it dies with a cryptic error message. */ + kill_guest(lg, "unhandled trap %li at %#lx (%#lx)", + lg->regs->trapnum, lg->regs->eip, + lg->regs->trapnum == 14 ? cr2 : lg->regs->errcode); + } + /* The Guest is dead => "No such file or directory" */ + return -ENOENT; +} + +/* Now we can look at each of the routines this calls, in increasing order of + * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(), + * deliver_trap() and demand_page(). After all those, we'll be ready to + * examine the Switcher, and our philosophical understanding of the Host/Guest + * duality will be complete. :*/ + +int find_free_guest(void) +{ + unsigned int i; + for (i = 0; i < MAX_LGUEST_GUESTS; i++) + if (!lguests[i].tsk) + return i; + return -1; +} + +static void adjust_pge(void *on) +{ + if (on) + write_cr4(read_cr4() | X86_CR4_PGE); + else + write_cr4(read_cr4() & ~X86_CR4_PGE); +} + +/*H:000 + * Welcome to the Host! + * + * By this point your brain has been tickled by the Guest code and numbed by + * the Launcher code; prepare for it to be stretched by the Host code. This is + * the heart. Let's begin at the initialization routine for the Host's lg + * module. + */ +static int __init init(void) +{ + int err; + + /* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */ + if (paravirt_enabled()) { + printk("lguest is afraid of %s\n", paravirt_ops.name); + return -EPERM; + } + + /* First we put the Switcher up in very high virtual memory. */ + err = map_switcher(); + if (err) + return err; + + /* Now we set up the pagetable implementation for the Guests. */ + err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES); + if (err) { + unmap_switcher(); + return err; + } + + /* The I/O subsystem needs some things initialized. */ + lguest_io_init(); + + /* /dev/lguest needs to be registered. */ + err = lguest_device_init(); + if (err) { + free_pagetables(); + unmap_switcher(); + return err; + } + + /* Finally, we need to turn off "Page Global Enable". PGE is an + * optimization where page table entries are specially marked to show + * they never change. The Host kernel marks all the kernel pages this + * way because it's always present, even when userspace is running. + * + * Lguest breaks this: unbeknownst to the rest of the Host kernel, we + * switch to the Guest kernel. If you don't disable this on all CPUs, + * you'll get really weird bugs that you'll chase for two days. + * + * I used to turn PGE off every time we switched to the Guest and back + * on when we return, but that slowed the Switcher down noticibly. */ + + /* We don't need the complexity of CPUs coming and going while we're + * doing this. */ + lock_cpu_hotplug(); + if (cpu_has_pge) { /* We have a broader idea of "global". */ + /* Remember that this was originally set (for cleanup). */ + cpu_had_pge = 1; + /* adjust_pge is a helper function which sets or unsets the PGE + * bit on its CPU, depending on the argument (0 == unset). */ + on_each_cpu(adjust_pge, (void *)0, 0, 1); + /* Turn off the feature in the global feature set. */ + clear_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability); + } + unlock_cpu_hotplug(); + + /* All good! */ + return 0; +} + +/* Cleaning up is just the same code, backwards. With a little French. */ +static void __exit fini(void) +{ + lguest_device_remove(); + free_pagetables(); + unmap_switcher(); + + /* If we had PGE before we started, turn it back on now. */ + lock_cpu_hotplug(); + if (cpu_had_pge) { + set_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability); + /* adjust_pge's argument "1" means set PGE. */ + on_each_cpu(adjust_pge, (void *)1, 0, 1); + } + unlock_cpu_hotplug(); +} + +/* The Host side of lguest can be a module. This is a nice way for people to + * play with it. */ +module_init(init); +module_exit(fini); +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>"); diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c new file mode 100644 index 00000000000..db6caace3b9 --- /dev/null +++ b/drivers/lguest/hypercalls.c @@ -0,0 +1,300 @@ +/*P:500 Just as userspace programs request kernel operations through a system + * call, the Guest requests Host operations through a "hypercall". You might + * notice this nomenclature doesn't really follow any logic, but the name has + * been around for long enough that we're stuck with it. As you'd expect, this + * code is basically a one big switch statement. :*/ + +/* Copyright (C) 2006 Rusty Russell IBM Corporation + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA +*/ +#include <linux/uaccess.h> +#include <linux/syscalls.h> +#include <linux/mm.h> +#include <asm/page.h> +#include <asm/pgtable.h> +#include <irq_vectors.h> +#include "lg.h" + +/*H:120 This is the core hypercall routine: where the Guest gets what it + * wants. Or gets killed. Or, in the case of LHCALL_CRASH, both. + * + * Remember from the Guest: %eax == which call to make, and the arguments are + * packed into %edx, %ebx and %ecx if needed. */ +static void do_hcall(struct lguest *lg, struct lguest_regs *regs) +{ + switch (regs->eax) { + case LHCALL_FLUSH_ASYNC: + /* This call does nothing, except by breaking out of the Guest + * it makes us process all the asynchronous hypercalls. */ + break; + case LHCALL_LGUEST_INIT: + /* You can't get here unless you're already initialized. Don't + * do that. */ + kill_guest(lg, "already have lguest_data"); + break; + case LHCALL_CRASH: { + /* Crash is such a trivial hypercall that we do it in four + * lines right here. */ + char msg[128]; + /* If the lgread fails, it will call kill_guest() itself; the + * kill_guest() with the message will be ignored. */ + lgread(lg, msg, regs->edx, sizeof(msg)); + msg[sizeof(msg)-1] = '\0'; + kill_guest(lg, "CRASH: %s", msg); + break; + } + case LHCALL_FLUSH_TLB: + /* FLUSH_TLB comes in two flavors, depending on the + * argument: */ + if (regs->edx) + guest_pagetable_clear_all(lg); + else + guest_pagetable_flush_user(lg); + break; + case LHCALL_BIND_DMA: + /* BIND_DMA really wants four arguments, but it's the only call + * which does. So the Guest packs the number of buffers and + * the interrupt number into the final argument, and we decode + * it here. This can legitimately fail, since we currently + * place a limit on the number of DMA pools a Guest can have. + * So we return true or false from this call. */ + regs->eax = bind_dma(lg, regs->edx, regs->ebx, + regs->ecx >> 8, regs->ecx & 0xFF); + break; + + /* All these calls simply pass the arguments through to the right + * routines. */ + case LHCALL_SEND_DMA: + send_dma(lg, regs->edx, regs->ebx); + break; + case LHCALL_LOAD_GDT: + load_guest_gdt(lg, regs->edx, regs->ebx); + break; + case LHCALL_LOAD_IDT_ENTRY: + load_guest_idt_entry(lg, regs->edx, regs->ebx, regs->ecx); + break; + case LHCALL_NEW_PGTABLE: + guest_new_pagetable(lg, regs->edx); + break; + case LHCALL_SET_STACK: + guest_set_stack(lg, regs->edx, regs->ebx, regs->ecx); + break; + case LHCALL_SET_PTE: + guest_set_pte(lg, regs->edx, regs->ebx, mkgpte(regs->ecx)); + break; + case LHCALL_SET_PMD: + guest_set_pmd(lg, regs->edx, regs->ebx); + break; + case LHCALL_LOAD_TLS: + guest_load_tls(lg, regs->edx); + break; + case LHCALL_SET_CLOCKEVENT: + guest_set_clockevent(lg, regs->edx); + break; + + case LHCALL_TS: + /* This sets the TS flag, as we saw used in run_guest(). */ + lg->ts = regs->edx; + break; + case LHCALL_HALT: + /* Similarly, this sets the halted flag for run_guest(). */ + lg->halted = 1; + break; + default: + kill_guest(lg, "Bad hypercall %li\n", regs->eax); + } +} + +/* Asynchronous hypercalls are easy: we just look in the array in the Guest's + * "struct lguest_data" and see if there are any new ones marked "ready". + * + * We are careful to do these in order: obviously we respect the order the + * Guest put them in the ring, but we also promise the Guest that they will + * happen before any normal hypercall (which is why we check this before + * checking for a normal hcall). */ +static void do_async_hcalls(struct lguest *lg) +{ + unsigned int i; + u8 st[LHCALL_RING_SIZE]; + + /* For simplicity, we copy the entire call status array in at once. */ + if (copy_from_user(&st, &lg->lguest_data->hcall_status, sizeof(st))) + return; + + + /* We process "struct lguest_data"s hcalls[] ring once. */ + for (i = 0; i < ARRAY_SIZE(st); i++) { + struct lguest_regs regs; + /* We remember where we were up to from last time. This makes + * sure that the hypercalls are done in the order the Guest + * places them in the ring. */ + unsigned int n = lg->next_hcall; + + /* 0xFF means there's no call here (yet). */ + if (st[n] == 0xFF) + break; + + /* OK, we have hypercall. Increment the "next_hcall" cursor, + * and wrap back to 0 if we reach the end. */ + if (++lg->next_hcall == LHCALL_RING_SIZE) + lg->next_hcall = 0; + + /* We copy the hypercall arguments into a fake register + * structure. This makes life simple for do_hcall(). */ + if (get_user(regs.eax, &lg->lguest_data->hcalls[n].eax) + || get_user(regs.edx, &lg->lguest_data->hcalls[n].edx) + || get_user(regs.ecx, &lg->lguest_data->hcalls[n].ecx) + || get_user(regs.ebx, &lg->lguest_data->hcalls[n].ebx)) { + kill_guest(lg, "Fetching async hypercalls"); + break; + } + + /* Do the hypercall, same as a normal one. */ + do_hcall(lg, ®s); + + /* Mark the hypercall done. */ + if (put_user(0xFF, &lg->lguest_data->hcall_status[n])) { + kill_guest(lg, "Writing result for async hypercall"); + break; + } + + /* Stop doing hypercalls if we've just done a DMA to the + * Launcher: it needs to service this first. */ + if (lg->dma_is_pending) + break; + } +} + +/* Last of all, we look at what happens first of all. The very first time the + * Guest makes a hypercall, we end up here to set things up: */ +static void initialize(struct lguest *lg) +{ + u32 tsc_speed; + + /* You can't do anything until you're initialized. The Guest knows the + * rules, so we're unforgiving here. */ + if (lg->regs->eax != LHCALL_LGUEST_INIT) { + kill_guest(lg, "hypercall %li before LGUEST_INIT", + lg->regs->eax); + return; + } + + /* We insist that the Time Stamp Counter exist and doesn't change with + * cpu frequency. Some devious chip manufacturers decided that TSC + * changes could be handled in software. I decided that time going + * backwards might be good for benchmarks, but it's bad for users. + * + * We also insist that the TSC be stable: the kernel detects unreliable + * TSCs for its own purposes, and we use that here. */ + if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && !check_tsc_unstable()) + tsc_speed = tsc_khz; + else + tsc_speed = 0; + + /* The pointer to the Guest's "struct lguest_data" is the only + * argument. */ + lg->lguest_data = (struct lguest_data __user *)lg->regs->edx; + /* If we check the address they gave is OK now, we can simply + * copy_to_user/from_user from now on rather than using lgread/lgwrite. + * I put this in to show that I'm not immune to writing stupid + * optimizations. */ + if (!lguest_address_ok(lg, lg->regs->edx, sizeof(*lg->lguest_data))) { + kill_guest(lg, "bad guest page %p", lg->lguest_data); + return; + } + /* The Guest tells us where we're not to deliver interrupts by putting + * the range of addresses into "struct lguest_data". */ + if (get_user(lg->noirq_start, &lg->lguest_data->noirq_start) + || get_user(lg->noirq_end, &lg->lguest_data->noirq_end) + /* We tell the Guest that it can't use the top 4MB of virtual + * addresses used by the Switcher. */ + || put_user(4U*1024*1024, &lg->lguest_data->reserve_mem) + || put_user(tsc_speed, &lg->lguest_data->tsc_khz) + /* We also give the Guest a unique id, as used in lguest_net.c. */ + || put_user(lg->guestid, &lg->lguest_data->guestid)) + kill_guest(lg, "bad guest page %p", lg->lguest_data); + + /* We write the current time into the Guest's data page once now. */ + write_timestamp(lg); + + /* This is the one case where the above accesses might have been the + * first write to a Guest page. This may have caused a copy-on-write + * fault, but the Guest might be referring to the old (read-only) + * page. */ + guest_pagetable_clear_all(lg); +} +/* Now we've examined the hypercall code; our Guest can make requests. There + * is one other way we can do things for the Guest, as we see in + * emulate_insn(). */ + +/*H:110 Tricky point: we mark the hypercall as "done" once we've done it. + * Normally we don't need to do this: the Guest will run again and update the + * trap number before we come back around the run_guest() loop to + * do_hypercalls(). + * + * However, if we are signalled or the Guest sends DMA to the Launcher, that + * loop will exit without running the Guest. When it comes back it would try + * to re-run the hypercall. */ +static void clear_hcall(struct lguest *lg) +{ + lg->regs->trapnum = 255; +} + +/*H:100 + * Hypercalls + * + * Remember from the Guest, hypercalls come in two flavors: normal and + * asynchronous. This file handles both of types. + */ +void do_hypercalls(struct lguest *lg) +{ + /* Not initialized yet? */ + if (unlikely(!lg->lguest_data)) { + /* Did the Guest make a hypercall? We might have come back for + * some other reason (an interrupt, a different trap). */ + if (lg->regs->trapnum == LGUEST_TRAP_ENTRY) { + /* Set up the "struct lguest_data" */ + initialize(lg); + /* The hypercall is done. */ + clear_hcall(lg); + } + return; + } + + /* The Guest has initialized. + * + * Look in the hypercall ring for the async hypercalls: */ + do_async_hcalls(lg); + + /* If we stopped reading the hypercall ring because the Guest did a + * SEND_DMA to the Launcher, we want to return now. Otherwise if the + * Guest asked us to do a hypercall, we do it. */ + if (!lg->dma_is_pending && lg->regs->trapnum == LGUEST_TRAP_ENTRY) { + do_hcall(lg, lg->regs); + /* The hypercall is done. */ + clear_hcall(lg); + } +} + +/* This routine supplies the Guest with time: it's used for wallclock time at + * initial boot and as a rough time source if the TSC isn't available. */ +void write_timestamp(struct lguest *lg) +{ + struct timespec now; + ktime_get_real_ts(&now); + if (put_user(now, &lg->lguest_data->time)) + kill_guest(lg, "Writing timestamp"); +} diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c new file mode 100644 index 00000000000..39731232d82 --- /dev/null +++ b/drivers/lguest/interrupts_and_traps.c @@ -0,0 +1,446 @@ +/*P:800 Interrupts (traps) are complicated enough to earn their own file. + * There are three classes of interrupts: + * + * 1) Real hardware interrupts which occur while we're running the Guest, + * 2) Interrupts for virtual devices attached to the Guest, and + * 3) Traps and faults from the Guest. + * + * Real hardware interrupts must be delivered to the Host, not the Guest. + * Virtual interrupts must be delivered to the Guest, but we make them look + * just like real hardware would deliver them. Traps from the Guest can be set + * up to go directly back into the Guest, but sometimes the Host wants to see + * them first, so we also have a way of "reflecting" them into the Guest as if + * they had been delivered to it directly. :*/ +#include <linux/uaccess.h> +#include "lg.h" + +/* The address of the interrupt handler is split into two bits: */ +static unsigned long idt_address(u32 lo, u32 hi) +{ + return (lo & 0x0000FFFF) | (hi & 0xFFFF0000); +} + +/* The "type" of the interrupt handler is a 4 bit field: we only support a + * couple of types. */ +static int idt_type(u32 lo, u32 hi) +{ + return (hi >> 8) & 0xF; +} + +/* An IDT entry can't be used unless the "present" bit is set. */ +static int idt_present(u32 lo, u32 hi) +{ + return (hi & 0x8000); +} + +/* We need a helper to "push" a value onto the Guest's stack, since that's a + * big part of what delivering an interrupt does. */ +static void push_guest_stack(struct lguest *lg, unsigned long *gstack, u32 val) +{ + /* Stack grows upwards: move stack then write value. */ + *gstack -= 4; + lgwrite_u32(lg, *gstack, val); +} + +/*H:210 The set_guest_interrupt() routine actually delivers the interrupt or + * trap. The mechanics of delivering traps and interrupts to the Guest are the + * same, except some traps have an "error code" which gets pushed onto the + * stack as well: the caller tells us if this is one. + * + * "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this + * interrupt or trap. It's split into two parts for traditional reasons: gcc + * on i386 used to be frightened by 64 bit numbers. + * + * We set up the stack just like the CPU does for a real interrupt, so it's + * identical for the Guest (and the standard "iret" instruction will undo + * it). */ +static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err) +{ + unsigned long gstack; + u32 eflags, ss, irq_enable; + + /* There are two cases for interrupts: one where the Guest is already + * in the kernel, and a more complex one where the Guest is in + * userspace. We check the privilege level to find out. */ + if ((lg->regs->ss&0x3) != GUEST_PL) { + /* The Guest told us their kernel stack with the SET_STACK + * hypercall: both the virtual address and the segment */ + gstack = guest_pa(lg, lg->esp1); + ss = lg->ss1; + /* We push the old stack segment and pointer onto the new + * stack: when the Guest does an "iret" back from the interrupt + * handler the CPU will notice they're dropping privilege + * levels and expect these here. */ + push_guest_stack(lg, &gstack, lg->regs->ss); + push_guest_stack(lg, &gstack, lg->regs->esp); + } else { + /* We're staying on the same Guest (kernel) stack. */ + gstack = guest_pa(lg, lg->regs->esp); + ss = lg->regs->ss; + } + + /* Remember that we never let the Guest actually disable interrupts, so + * the "Interrupt Flag" bit is always set. We copy that bit from the + * Guest's "irq_enabled" field into the eflags word: the Guest copies + * it back in "lguest_iret". */ + eflags = lg->regs->eflags; + if (get_user(irq_enable, &lg->lguest_data->irq_enabled) == 0 + && !(irq_enable & X86_EFLAGS_IF)) + eflags &= ~X86_EFLAGS_IF; + + /* An interrupt is expected to push three things on the stack: the old + * "eflags" word, the old code segment, and the old instruction + * pointer. */ + push_guest_stack(lg, &gstack, eflags); + push_guest_stack(lg, &gstack, lg->regs->cs); + push_guest_stack(lg, &gstack, lg->regs->eip); + + /* For the six traps which supply an error code, we push that, too. */ + if (has_err) + push_guest_stack(lg, &gstack, lg->regs->errcode); + + /* Now we've pushed all the old state, we change the stack, the code + * segment and the address to execute. */ + lg->regs->ss = ss; + lg->regs->esp = gstack + lg->page_offset; + lg->regs->cs = (__KERNEL_CS|GUEST_PL); + lg->regs->eip = idt_address(lo, hi); + + /* There are two kinds of interrupt handlers: 0xE is an "interrupt + * gate" which expects interrupts to be disabled on entry. */ + if (idt_type(lo, hi) == 0xE) + if (put_user(0, &lg->lguest_data->irq_enabled)) + kill_guest(lg, "Disabling interrupts"); +} + +/*H:200 + * Virtual Interrupts. + * + * maybe_do_interrupt() gets called before every entry to the Guest, to see if + * we should divert the Guest to running an interrupt handler. */ +void maybe_do_interrupt(struct lguest *lg) +{ + unsigned int irq; + DECLARE_BITMAP(blk, LGUEST_IRQS); + struct desc_struct *idt; + + /* If the Guest hasn't even initialized yet, we can do nothing. */ + if (!lg->lguest_data) + return; + + /* Take our "irqs_pending" array and remove any interrupts the Guest + * wants blocked: the result ends up in "blk". */ + if (copy_from_user(&blk, lg->lguest_data->blocked_interrupts, + sizeof(blk))) + return; + + bitmap_andnot(blk, lg->irqs_pending, blk, LGUEST_IRQS); + + /* Find the first interrupt. */ + irq = find_first_bit(blk, LGUEST_IRQS); + /* None? Nothing to do */ + if (irq >= LGUEST_IRQS) + return; + + /* They may be in the middle of an iret, where they asked us never to + * deliver interrupts. */ + if (lg->regs->eip >= lg->noirq_start && lg->regs->eip < lg->noirq_end) + return; + + /* If they're halted, interrupts restart them. */ + if (lg->halted) { + /* Re-enable interrupts. */ + if (put_user(X86_EFLAGS_IF, &lg->lguest_data->irq_enabled)) + kill_guest(lg, "Re-enabling interrupts"); + lg->halted = 0; + } else { + /* Otherwise we check if they have interrupts disabled. */ + u32 irq_enabled; + if (get_user(irq_enabled, &lg->lguest_data->irq_enabled)) + irq_enabled = 0; + if (!irq_enabled) + return; + } + + /* Look at the IDT entry the Guest gave us for this interrupt. The + * first 32 (FIRST_EXTERNAL_VECTOR) entries are for traps, so we skip + * over them. */ + idt = &lg->idt[FIRST_EXTERNAL_VECTOR+irq]; + /* If they don't have a handler (yet?), we just ignore it */ + if (idt_present(idt->a, idt->b)) { + /* OK, mark it no longer pending and deliver it. */ + clear_bit(irq, lg->irqs_pending); + /* set_guest_interrupt() takes the interrupt descriptor and a + * flag to say whether this interrupt pushes an error code onto + * the stack as well: virtual interrupts never do. */ + set_guest_interrupt(lg, idt->a, idt->b, 0); + } + + /* Every time we deliver an interrupt, we update the timestamp in the + * Guest's lguest_data struct. It would be better for the Guest if we + * did this more often, but it can actually be quite slow: doing it + * here is a compromise which means at least it gets updated every + * timer interrupt. */ + write_timestamp(lg); +} + +/*H:220 Now we've got the routines to deliver interrupts, delivering traps + * like page fault is easy. The only trick is that Intel decided that some + * traps should have error codes: */ +static int has_err(unsigned int trap) +{ + return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17); +} + +/* deliver_trap() returns true if it could deliver the trap. */ +int deliver_trap(struct lguest *lg, unsigned int num) +{ + /* Trap numbers are always 8 bit, but we set an impossible trap number + * for traps inside the Switcher, so check that here. */ + if (num >= ARRAY_SIZE(lg->idt)) + return 0; + + /* Early on the Guest hasn't set the IDT entries (or maybe it put a + * bogus one in): if we fail here, the Guest will be killed. */ + if (!idt_present(lg->idt[num].a, lg->idt[num].b)) + return 0; + set_guest_interrupt(lg, lg->idt[num].a, lg->idt[num].b, has_err(num)); + return 1; +} + +/*H:250 Here's the hard part: returning to the Host every time a trap happens + * and then calling deliver_trap() and re-entering the Guest is slow. + * Particularly because Guest userspace system calls are traps (trap 128). + * + * So we'd like to set up the IDT to tell the CPU to deliver traps directly + * into the Guest. This is possible, but the complexities cause the size of + * this file to double! However, 150 lines of code is worth writing for taking + * system calls down from 1750ns to 270ns. Plus, if lguest didn't do it, all + * the other hypervisors would tease it. + * + * This routine determines if a trap can be delivered directly. */ +static int direct_trap(const struct lguest *lg, + const struct desc_struct *trap, + unsigned int num) +{ + /* Hardware interrupts don't go to the Guest at all (except system + * call). */ + if (num >= FIRST_EXTERNAL_VECTOR && num != SYSCALL_VECTOR) + return 0; + + /* The Host needs to see page faults (for shadow paging and to save the + * fault address), general protection faults (in/out emulation) and + * device not available (TS handling), and of course, the hypercall + * trap. */ + if (num == 14 || num == 13 || num == 7 || num == LGUEST_TRAP_ENTRY) + return 0; + + /* Only trap gates (type 15) can go direct to the Guest. Interrupt + * gates (type 14) disable interrupts as they are entered, which we + * never let the Guest do. Not present entries (type 0x0) also can't + * go direct, of course 8) */ + return idt_type(trap->a, trap->b) == 0xF; +} +/*:*/ + +/*M:005 The Guest has the ability to turn its interrupt gates into trap gates, + * if it is careful. The Host will let trap gates can go directly to the + * Guest, but the Guest needs the interrupts atomically disabled for an + * interrupt gate. It can do this by pointing the trap gate at instructions + * within noirq_start and noirq_end, where it can safely disable interrupts. */ + +/*M:006 The Guests do not use the sysenter (fast system call) instruction, + * because it's hardcoded to enter privilege level 0 and so can't go direct. + * It's about twice as fast as the older "int 0x80" system call, so it might + * still be worthwhile to handle it in the Switcher and lcall down to the + * Guest. The sysenter semantics are hairy tho: search for that keyword in + * entry.S :*/ + +/*H:260 When we make traps go directly into the Guest, we need to make sure + * the kernel stack is valid (ie. mapped in the page tables). Otherwise, the + * CPU trying to deliver the trap will fault while trying to push the interrupt + * words on the stack: this is called a double fault, and it forces us to kill + * the Guest. + * + * Which is deeply unfair, because (literally!) it wasn't the Guests' fault. */ +void pin_stack_pages(struct lguest *lg) +{ + unsigned int i; + + /* Depending on the CONFIG_4KSTACKS option, the Guest can have one or + * two pages of stack space. */ + for (i = 0; i < lg->stack_pages; i++) + /* The stack grows *upwards*, so the address we're given is the + * start of the page after the kernel stack. Subtract one to + * get back onto the first stack page, and keep subtracting to + * get to the rest of the stack pages. */ + pin_page(lg, lg->esp1 - 1 - i * PAGE_SIZE); +} + +/* Direct traps also mean that we need to know whenever the Guest wants to use + * a different kernel stack, so we can change the IDT entries to use that + * stack. The IDT entries expect a virtual address, so unlike most addresses + * the Guest gives us, the "esp" (stack pointer) value here is virtual, not + * physical. + * + * In Linux each process has its own kernel stack, so this happens a lot: we + * change stacks on each context switch. */ +void guest_set_stack(struct lguest *lg, u32 seg, u32 esp, unsigned int pages) +{ + /* You are not allowd have a stack segment with privilege level 0: bad + * Guest! */ + if ((seg & 0x3) != GUEST_PL) + kill_guest(lg, "bad stack segment %i", seg); + /* We only expect one or two stack pages. */ + if (pages > 2) + kill_guest(lg, "bad stack pages %u", pages); + /* Save where the stack is, and how many pages */ + lg->ss1 = seg; + lg->esp1 = esp; + lg->stack_pages = pages; + /* Make sure the new stack pages are mapped */ + pin_stack_pages(lg); +} + +/* All this reference to mapping stacks leads us neatly into the other complex + * part of the Host: page table handling. */ + +/*H:235 This is the routine which actually checks the Guest's IDT entry and + * transfers it into our entry in "struct lguest": */ +static void set_trap(struct lguest *lg, struct desc_struct *trap, + unsigned int num, u32 lo, u32 hi) +{ + u8 type = idt_type(lo, hi); + + /* We zero-out a not-present entry */ + if (!idt_present(lo, hi)) { + trap->a = trap->b = 0; + return; + } + + /* We only support interrupt and trap gates. */ + if (type != 0xE && type != 0xF) + kill_guest(lg, "bad IDT type %i", type); + + /* We only copy the handler address, present bit, privilege level and + * type. The privilege level controls where the trap can be triggered + * manually with an "int" instruction. This is usually GUEST_PL, + * except for system calls which userspace can use. */ + trap->a = ((__KERNEL_CS|GUEST_PL)<<16) | (lo&0x0000FFFF); + trap->b = (hi&0xFFFFEF00); +} + +/*H:230 While we're here, dealing with delivering traps and interrupts to the + * Guest, we might as well complete the picture: how the Guest tells us where + * it wants them to go. This would be simple, except making traps fast + * requires some tricks. + * + * We saw the Guest setting Interrupt Descriptor Table (IDT) entries with the + * LHCALL_LOAD_IDT_ENTRY hypercall before: that comes here. */ +void load_guest_idt_entry(struct lguest *lg, unsigned int num, u32 lo, u32 hi) +{ + /* Guest never handles: NMI, doublefault, spurious interrupt or + * hypercall. We ignore when it tries to set them. */ + if (num == 2 || num == 8 || num == 15 || num == LGUEST_TRAP_ENTRY) + return; + + /* Mark the IDT as changed: next time the Guest runs we'll know we have + * to copy this again. */ + lg->changed |= CHANGED_IDT; + + /* The IDT which we keep in "struct lguest" only contains 32 entries + * for the traps and LGUEST_IRQS (32) entries for interrupts. We + * ignore attempts to set handlers for higher interrupt numbers, except + * for the system call "interrupt" at 128: we have a special IDT entry + * for that. */ + if (num < ARRAY_SIZE(lg->idt)) + set_trap(lg, &lg->idt[num], num, lo, hi); + else if (num == SYSCALL_VECTOR) + set_trap(lg, &lg->syscall_idt, num, lo, hi); +} + +/* The default entry for each interrupt points into the Switcher routines which + * simply return to the Host. The run_guest() loop will then call + * deliver_trap() to bounce it back into the Guest. */ +static void default_idt_entry(struct desc_struct *idt, + int trap, + const unsigned long handler) +{ + /* A present interrupt gate. */ + u32 flags = 0x8e00; + + /* Set the privilege level on the entry for the hypercall: this allows + * the Guest to use the "int" instruction to trigger it. */ + if (trap == LGUEST_TRAP_ENTRY) + flags |= (GUEST_PL << 13); + + /* Now pack it into the IDT entry in its weird format. */ + idt->a = (LGUEST_CS<<16) | (handler&0x0000FFFF); + idt->b = (handler&0xFFFF0000) | flags; +} + +/* When the Guest first starts, we put default entries into the IDT. */ +void setup_default_idt_entries(struct lguest_ro_state *state, + const unsigned long *def) +{ + unsigned int i; + + for (i = 0; i < ARRAY_SIZE(state->guest_idt); i++) + default_idt_entry(&state->guest_idt[i], i, def[i]); +} + +/*H:240 We don't use the IDT entries in the "struct lguest" directly, instead + * we copy them into the IDT which we've set up for Guests on this CPU, just + * before we run the Guest. This routine does that copy. */ +void copy_traps(const struct lguest *lg, struct desc_struct *idt, + const unsigned long *def) +{ + unsigned int i; + + /* We can simply copy the direct traps, otherwise we use the default + * ones in the Switcher: they will return to the Host. */ + for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++) { + if (direct_trap(lg, &lg->idt[i], i)) + idt[i] = lg->idt[i]; + else + default_idt_entry(&idt[i], i, def[i]); + } + + /* Don't forget the system call trap! The IDT entries for other + * interupts never change, so no need to copy them. */ + i = SYSCALL_VECTOR; + if (direct_trap(lg, &lg->syscall_idt, i)) + idt[i] = lg->syscall_idt; + else + default_idt_entry(&idt[i], i, def[i]); +} + +void guest_set_clockevent(struct lguest *lg, unsigned long delta) +{ + ktime_t expires; + + if (unlikely(delta == 0)) { + /* Clock event device is shutting down. */ + hrtimer_cancel(&lg->hrt); + return; + } + + expires = ktime_add_ns(ktime_get_real(), delta); + hrtimer_start(&lg->hrt, expires, HRTIMER_MODE_ABS); +} + +static enum hrtimer_restart clockdev_fn(struct hrtimer *timer) +{ + struct lguest *lg = container_of(timer, struct lguest, hrt); + + set_bit(0, lg->irqs_pending); + if (lg->halted) + wake_up_process(lg->tsk); + return HRTIMER_NORESTART; +} + +void init_clockdev(struct lguest *lg) +{ + hrtimer_init(&lg->hrt, CLOCK_REALTIME, HRTIMER_MODE_ABS); + lg->hrt.function = clockdev_fn; +} diff --git a/drivers/lguest/io.c b/drivers/lguest/io.c new file mode 100644 index 00000000000..ea68613b43f --- /dev/null +++ b/drivers/lguest/io.c @@ -0,0 +1,626 @@ +/*P:300 The I/O mechanism in lguest is simple yet flexible, allowing the Guest + * to talk to the Launcher or directly to another Guest. It uses familiar + * concepts of DMA and interrupts, plus some neat code stolen from + * futexes... :*/ + +/* Copyright (C) 2006 Rusty Russell IBM Corporation + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + */ +#include <linux/types.h> +#include <linux/futex.h> +#include <linux/jhash.h> +#include <linux/mm.h> +#include <linux/highmem.h> +#include <linux/uaccess.h> +#include "lg.h" + +/*L:300 + * I/O + * + * Getting data in and out of the Guest is quite an art. There are numerous + * ways to do it, and they all suck differently. We try to keep things fairly + * close to "real" hardware so our Guest's drivers don't look like an alien + * visitation in the middle of the Linux code, and yet make sure that Guests + * can talk directly to other Guests, not just the Launcher. + * + * To do this, the Guest gives us a key when it binds or sends DMA buffers. + * The key corresponds to a "physical" address inside the Guest (ie. a virtual + * address inside the Launcher process). We don't, however, use this key + * directly. + * + * We want Guests which share memory to be able to DMA to each other: two + * Launchers can mmap memory the same file, then the Guests can communicate. + * Fortunately, the futex code provides us with a way to get a "union + * futex_key" corresponding to the memory lying at a virtual address: if the + * two processes share memory, the "union futex_key" for that memory will match + * even if the memory is mapped at different addresses in each. So we always + * convert the keys to "union futex_key"s to compare them. + * + * Before we dive into this though, we need to look at another set of helper + * routines used throughout the Host kernel code to access Guest memory. + :*/ +static struct list_head dma_hash[61]; + +/* An unfortunate side effect of the Linux double-linked list implementation is + * that there's no good way to statically initialize an array of linked + * lists. */ +void lguest_io_init(void) +{ + unsigned int i; + + for (i = 0; i < ARRAY_SIZE(dma_hash); i++) + INIT_LIST_HEAD(&dma_hash[i]); +} + +/* FIXME: allow multi-page lengths. */ +static int check_dma_list(struct lguest *lg, const struct lguest_dma *dma) +{ + unsigned int i; + + for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) { + if (!dma->len[i]) + return 1; + if (!lguest_address_ok(lg, dma->addr[i], dma->len[i])) + goto kill; + if (dma->len[i] > PAGE_SIZE) + goto kill; + /* We could do over a page, but is it worth it? */ + if ((dma->addr[i] % PAGE_SIZE) + dma->len[i] > PAGE_SIZE) + goto kill; + } + return 1; + +kill: + kill_guest(lg, "bad DMA entry: %u@%#lx", dma->len[i], dma->addr[i]); + return 0; +} + +/*L:330 This is our hash function, using the wonderful Jenkins hash. + * + * The futex key is a union with three parts: an unsigned long word, a pointer, + * and an int "offset". We could use jhash_2words() which takes three u32s. + * (Ok, the hash functions are great: the naming sucks though). + * + * It's nice to be portable to 64-bit platforms, so we use the more generic + * jhash2(), which takes an array of u32, the number of u32s, and an initial + * u32 to roll in. This is uglier, but breaks down to almost the same code on + * 32-bit platforms like this one. + * + * We want a position in the array, so we modulo ARRAY_SIZE(dma_hash) (ie. 61). + */ +static unsigned int hash(const union futex_key *key) +{ + return jhash2((u32*)&key->both.word, + (sizeof(key->both.word)+sizeof(key->both.ptr))/4, + key->both.offset) + % ARRAY_SIZE(dma_hash); +} + +/* This is a convenience routine to compare two keys. It's a much bemoaned C + * weakness that it doesn't allow '==' on structures or unions, so we have to + * open-code it like this. */ +static inline int key_eq(const union futex_key *a, const union futex_key *b) +{ + return (a->both.word == b->both.word + && a->both.ptr == b->both.ptr + && a->both.offset == b->both.offset); +} + +/*L:360 OK, when we need to actually free up a Guest's DMA array we do several + * things, so we have a convenient function to do it. + * + * The caller must hold a read lock on dmainfo owner's current->mm->mmap_sem + * for the drop_futex_key_refs(). */ +static void unlink_dma(struct lguest_dma_info *dmainfo) +{ + /* You locked this too, right? */ + BUG_ON(!mutex_is_locked(&lguest_lock)); + /* This is how we know that the entry is free. */ + dmainfo->interrupt = 0; + /* Remove it from the hash table. */ + list_del(&dmainfo->list); + /* Drop the references we were holding (to the inode or mm). */ + drop_futex_key_refs(&dmainfo->key); +} + +/*L:350 This is the routine which we call when the Guest asks to unregister a + * DMA array attached to a given key. Returns true if the array was found. */ +static int unbind_dma(struct lguest *lg, + const union futex_key *key, + unsigned long dmas) +{ + int i, ret = 0; + + /* We don't bother with the hash table, just look through all this + * Guest's DMA arrays. */ + for (i = 0; i < LGUEST_MAX_DMA; i++) { + /* In theory it could have more than one array on the same key, + * or one array on multiple keys, so we check both */ + if (key_eq(key, &lg->dma[i].key) && dmas == lg->dma[i].dmas) { + unlink_dma(&lg->dma[i]); + ret = 1; + break; + } + } + return ret; +} + +/*L:340 BIND_DMA: this is the hypercall which sets up an array of "struct + * lguest_dma" for receiving I/O. + * + * The Guest wants to bind an array of "struct lguest_dma"s to a particular key + * to receive input. This only happens when the Guest is setting up a new + * device, so it doesn't have to be very fast. + * + * It returns 1 on a successful registration (it can fail if we hit the limit + * of registrations for this Guest). + */ +int bind_dma(struct lguest *lg, + unsigned long ukey, unsigned long dmas, u16 numdmas, u8 interrupt) +{ + unsigned int i; + int ret = 0; + union futex_key key; + /* Futex code needs the mmap_sem. */ + struct rw_semaphore *fshared = ¤t->mm->mmap_sem; + + /* Invalid interrupt? (We could kill the guest here). */ + if (interrupt >= LGUEST_IRQS) + return 0; + + /* We need to grab the Big Lguest Lock, because other Guests may be + * trying to look through this Guest's DMAs to send something while + * we're doing this. */ + mutex_lock(&lguest_lock); + down_read(fshared); + if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) { + kill_guest(lg, "bad dma key %#lx", ukey); + goto unlock; + } + + /* We want to keep this key valid once we drop mmap_sem, so we have to + * hold a reference. */ + get_futex_key_refs(&key); + + /* If the Guest specified an interrupt of 0, that means they want to + * unregister this array of "struct lguest_dma"s. */ + if (interrupt == 0) + ret = unbind_dma(lg, &key, dmas); + else { + /* Look through this Guest's dma array for an unused entry. */ + for (i = 0; i < LGUEST_MAX_DMA; i++) { + /* If the interrupt is non-zero, the entry is already + * used. */ + if (lg->dma[i].interrupt) + continue; + + /* OK, a free one! Fill on our details. */ + lg->dma[i].dmas = dmas; + lg->dma[i].num_dmas = numdmas; + lg->dma[i].next_dma = 0; + lg->dma[i].key = key; + lg->dma[i].guestid = lg->guestid; + lg->dma[i].interrupt = interrupt; + + /* Now we add it to the hash table: the position + * depends on the futex key that we got. */ + list_add(&lg->dma[i].list, &dma_hash[hash(&key)]); + /* Success! */ + ret = 1; + goto unlock; + } + } + /* If we didn't find a slot to put the key in, drop the reference + * again. */ + drop_futex_key_refs(&key); +unlock: + /* Unlock and out. */ + up_read(fshared); + mutex_unlock(&lguest_lock); + return ret; +} + +/*L:385 Note that our routines to access a different Guest's memory are called + * lgread_other() and lgwrite_other(): these names emphasize that they are only + * used when the Guest is *not* the current Guest. + * + * The interface for copying from another process's memory is called + * access_process_vm(), with a final argument of 0 for a read, and 1 for a + * write. + * + * We need lgread_other() to read the destination Guest's "struct lguest_dma" + * array. */ +static int lgread_other(struct lguest *lg, + void *buf, u32 addr, unsigned bytes) +{ + if (!lguest_address_ok(lg, addr, bytes) + || access_process_vm(lg->tsk, addr, buf, bytes, 0) != bytes) { + memset(buf, 0, bytes); + kill_guest(lg, "bad address in registered DMA struct"); + return 0; + } + return 1; +} + +/* "lgwrite()" to another Guest: used to update the destination "used_len" once + * we've transferred data into the buffer. */ +static int lgwrite_other(struct lguest *lg, u32 addr, + const void *buf, unsigned bytes) +{ + if (!lguest_address_ok(lg, addr, bytes) + || (access_process_vm(lg->tsk, addr, (void *)buf, bytes, 1) + != bytes)) { + kill_guest(lg, "bad address writing to registered DMA"); + return 0; + } + return 1; +} + +/*L:400 This is the generic engine which copies from a source "struct + * lguest_dma" from this Guest into another Guest's "struct lguest_dma". The + * destination Guest's pages have already been mapped, as contained in the + * pages array. + * + * If you're wondering if there's a nice "copy from one process to another" + * routine, so was I. But Linux isn't really set up to copy between two + * unrelated processes, so we have to write it ourselves. + */ +static u32 copy_data(struct lguest *srclg, + const struct lguest_dma *src, + const struct lguest_dma *dst, + struct page *pages[]) +{ + unsigned int totlen, si, di, srcoff, dstoff; + void *maddr = NULL; + + /* We return the total length transferred. */ + totlen = 0; + + /* We keep indexes into the source and destination "struct lguest_dma", + * and an offset within each region. */ + si = di = 0; + srcoff = dstoff = 0; + + /* We loop until the source or destination is exhausted. */ + while (si < LGUEST_MAX_DMA_SECTIONS && src->len[si] + && di < LGUEST_MAX_DMA_SECTIONS && dst->len[di]) { + /* We can only transfer the rest of the src buffer, or as much + * as will fit into the destination buffer. */ + u32 len = min(src->len[si] - srcoff, dst->len[di] - dstoff); + + /* For systems using "highmem" we need to use kmap() to access + * the page we want. We often use the same page over and over, + * so rather than kmap() it on every loop, we set the maddr + * pointer to NULL when we need to move to the next + * destination page. */ + if (!maddr) + maddr = kmap(pages[di]); + + /* Copy directly from (this Guest's) source address to the + * destination Guest's kmap()ed buffer. Note that maddr points + * to the start of the page: we need to add the offset of the + * destination address and offset within the buffer. */ + + /* FIXME: This is not completely portable. I looked at + * copy_to_user_page(), and some arch's seem to need special + * flushes. x86 is fine. */ + if (copy_from_user(maddr + (dst->addr[di] + dstoff)%PAGE_SIZE, + (void __user *)src->addr[si], len) != 0) { + /* If a copy failed, it's the source's fault. */ + kill_guest(srclg, "bad address in sending DMA"); + totlen = 0; + break; + } + + /* Increment the total and src & dst offsets */ + totlen += len; + srcoff += len; + dstoff += len; + + /* Presumably we reached the end of the src or dest buffers: */ + if (srcoff == src->len[si]) { + /* Move to the next buffer at offset 0 */ + si++; + srcoff = 0; + } + if (dstoff == dst->len[di]) { + /* We need to unmap that destination page and reset + * maddr ready for the next one. */ + kunmap(pages[di]); + maddr = NULL; + di++; + dstoff = 0; + } + } + + /* If we still had a page mapped at the end, unmap now. */ + if (maddr) + kunmap(pages[di]); + + return totlen; +} + +/*L:390 This is how we transfer a "struct lguest_dma" from the source Guest + * (the current Guest which called SEND_DMA) to another Guest. */ +static u32 do_dma(struct lguest *srclg, const struct lguest_dma *src, + struct lguest *dstlg, const struct lguest_dma *dst) +{ + int i; + u32 ret; + struct page *pages[LGUEST_MAX_DMA_SECTIONS]; + + /* We check that both source and destination "struct lguest_dma"s are + * within the bounds of the source and destination Guests */ + if (!check_dma_list(dstlg, dst) || !check_dma_list(srclg, src)) + return 0; + + /* We need to map the pages which correspond to each parts of + * destination buffer. */ + for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) { + if (dst->len[i] == 0) + break; + /* get_user_pages() is a complicated function, especially since + * we only want a single page. But it works, and returns the + * number of pages. Note that we're holding the destination's + * mmap_sem, as get_user_pages() requires. */ + if (get_user_pages(dstlg->tsk, dstlg->mm, + dst->addr[i], 1, 1, 1, pages+i, NULL) + != 1) { + /* This means the destination gave us a bogus buffer */ + kill_guest(dstlg, "Error mapping DMA pages"); + ret = 0; + goto drop_pages; + } + } + + /* Now copy the data until we run out of src or dst. */ + ret = copy_data(srclg, src, dst, pages); + +drop_pages: + while (--i >= 0) + put_page(pages[i]); + return ret; +} + +/*L:380 Transferring data from one Guest to another is not as simple as I'd + * like. We've found the "struct lguest_dma_info" bound to the same address as + * the send, we need to copy into it. + * + * This function returns true if the destination array was empty. */ +static int dma_transfer(struct lguest *srclg, + unsigned long udma, + struct lguest_dma_info *dst) +{ + struct lguest_dma dst_dma, src_dma; + struct lguest *dstlg; + u32 i, dma = 0; + + /* From the "struct lguest_dma_info" we found in the hash, grab the + * Guest. */ + dstlg = &lguests[dst->guestid]; + /* Read in the source "struct lguest_dma" handed to SEND_DMA. */ + lgread(srclg, &src_dma, udma, sizeof(src_dma)); + + /* We need the destination's mmap_sem, and we already hold the source's + * mmap_sem for the futex key lookup. Normally this would suggest that + * we could deadlock if the destination Guest was trying to send to + * this source Guest at the same time, which is another reason that all + * I/O is done under the big lguest_lock. */ + down_read(&dstlg->mm->mmap_sem); + + /* Look through the destination DMA array for an available buffer. */ + for (i = 0; i < dst->num_dmas; i++) { + /* We keep a "next_dma" pointer which often helps us avoid + * looking at lots of previously-filled entries. */ + dma = (dst->next_dma + i) % dst->num_dmas; + if (!lgread_other(dstlg, &dst_dma, + dst->dmas + dma * sizeof(struct lguest_dma), + sizeof(dst_dma))) { + goto fail; + } + if (!dst_dma.used_len) + break; + } + + /* If we found a buffer, we do the actual data copy. */ + if (i != dst->num_dmas) { + unsigned long used_lenp; + unsigned int ret; + + ret = do_dma(srclg, &src_dma, dstlg, &dst_dma); + /* Put used length in the source "struct lguest_dma"'s used_len + * field. It's a little tricky to figure out where that is, + * though. */ + lgwrite_u32(srclg, + udma+offsetof(struct lguest_dma, used_len), ret); + /* Tranferring 0 bytes is OK if the source buffer was empty. */ + if (ret == 0 && src_dma.len[0] != 0) + goto fail; + + /* The destination Guest might be running on a different CPU: + * we have to make sure that it will see the "used_len" field + * change to non-zero *after* it sees the data we copied into + * the buffer. Hence a write memory barrier. */ + wmb(); + /* Figuring out where the destination's used_len field for this + * "struct lguest_dma" in the array is also a little ugly. */ + used_lenp = dst->dmas + + dma * sizeof(struct lguest_dma) + + offsetof(struct lguest_dma, used_len); + lgwrite_other(dstlg, used_lenp, &ret, sizeof(ret)); + /* Move the cursor for next time. */ + dst->next_dma++; + } + up_read(&dstlg->mm->mmap_sem); + + /* We trigger the destination interrupt, even if the destination was + * empty and we didn't transfer anything: this gives them a chance to + * wake up and refill. */ + set_bit(dst->interrupt, dstlg->irqs_pending); + /* Wake up the destination process. */ + wake_up_process(dstlg->tsk); + /* If we passed the last "struct lguest_dma", the receive had no + * buffers left. */ + return i == dst->num_dmas; + +fail: + up_read(&dstlg->mm->mmap_sem); + return 0; +} + +/*L:370 This is the counter-side to the BIND_DMA hypercall; the SEND_DMA + * hypercall. We find out who's listening, and send to them. */ +void send_dma(struct lguest *lg, unsigned long ukey, unsigned long udma) +{ + union futex_key key; + int empty = 0; + struct rw_semaphore *fshared = ¤t->mm->mmap_sem; + +again: + mutex_lock(&lguest_lock); + down_read(fshared); + /* Get the futex key for the key the Guest gave us */ + if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) { + kill_guest(lg, "bad sending DMA key"); + goto unlock; + } + /* Since the key must be a multiple of 4, the futex key uses the lower + * bit of the "offset" field (which would always be 0) to indicate a + * mapping which is shared with other processes (ie. Guests). */ + if (key.shared.offset & 1) { + struct lguest_dma_info *i; + /* Look through the hash for other Guests. */ + list_for_each_entry(i, &dma_hash[hash(&key)], list) { + /* Don't send to ourselves. */ + if (i->guestid == lg->guestid) + continue; + if (!key_eq(&key, &i->key)) + continue; + + /* If dma_transfer() tells us the destination has no + * available buffers, we increment "empty". */ + empty += dma_transfer(lg, udma, i); + break; + } + /* If the destination is empty, we release our locks and + * give the destination Guest a brief chance to restock. */ + if (empty == 1) { + /* Give any recipients one chance to restock. */ + up_read(¤t->mm->mmap_sem); + mutex_unlock(&lguest_lock); + /* Next time, we won't try again. */ + empty++; + goto again; + } + } else { + /* Private mapping: Guest is sending to its Launcher. We set + * the "dma_is_pending" flag so that the main loop will exit + * and the Launcher's read() from /dev/lguest will return. */ + lg->dma_is_pending = 1; + lg->pending_dma = udma; + lg->pending_key = ukey; + } +unlock: + up_read(fshared); + mutex_unlock(&lguest_lock); +} +/*:*/ + +void release_all_dma(struct lguest *lg) +{ + unsigned int i; + + BUG_ON(!mutex_is_locked(&lguest_lock)); + + down_read(&lg->mm->mmap_sem); + for (i = 0; i < LGUEST_MAX_DMA; i++) { + if (lg->dma[i].interrupt) + unlink_dma(&lg->dma[i]); + } + up_read(&lg->mm->mmap_sem); +} + +/*M:007 We only return a single DMA buffer to the Launcher, but it would be + * more efficient to return a pointer to the entire array of DMA buffers, which + * it can cache and choose one whenever it wants. + * + * Currently the Launcher uses a write to /dev/lguest, and the return value is + * the address of the DMA structure with the interrupt number placed in + * dma->used_len. If we wanted to return the entire array, we need to return + * the address, array size and interrupt number: this seems to require an + * ioctl(). :*/ + +/*L:320 This routine looks for a DMA buffer registered by the Guest on the + * given key (using the BIND_DMA hypercall). */ +unsigned long get_dma_buffer(struct lguest *lg, + unsigned long ukey, unsigned long *interrupt) +{ + unsigned long ret = 0; + union futex_key key; + struct lguest_dma_info *i; + struct rw_semaphore *fshared = ¤t->mm->mmap_sem; + + /* Take the Big Lguest Lock to stop other Guests sending this Guest DMA + * at the same time. */ + mutex_lock(&lguest_lock); + /* To match between Guests sharing the same underlying memory we steal + * code from the futex infrastructure. This requires that we hold the + * "mmap_sem" for our process (the Launcher), and pass it to the futex + * code. */ + down_read(fshared); + + /* This can fail if it's not a valid address, or if the address is not + * divisible by 4 (the futex code needs that, we don't really). */ + if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) { + kill_guest(lg, "bad registered DMA buffer"); + goto unlock; + } + /* Search the hash table for matching entries (the Launcher can only + * send to its own Guest for the moment, so the entry must be for this + * Guest) */ + list_for_each_entry(i, &dma_hash[hash(&key)], list) { + if (key_eq(&key, &i->key) && i->guestid == lg->guestid) { + unsigned int j; + /* Look through the registered DMA array for an + * available buffer. */ + for (j = 0; j < i->num_dmas; j++) { + struct lguest_dma dma; + + ret = i->dmas + j * sizeof(struct lguest_dma); + lgread(lg, &dma, ret, sizeof(dma)); + if (dma.used_len == 0) + break; + } + /* Store the interrupt the Guest wants when the buffer + * is used. */ + *interrupt = i->interrupt; + break; + } + } +unlock: + up_read(fshared); + mutex_unlock(&lguest_lock); + return ret; +} +/*:*/ + +/*L:410 This really has completed the Launcher. Not only have we now finished + * the longest chapter in our journey, but this also means we are over halfway + * through! + * + * Enough prevaricating around the bush: it is time for us to dive into the + * core of the Host, in "make Host". + */ diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h new file mode 100644 index 00000000000..64f0abed317 --- /dev/null +++ b/drivers/lguest/lg.h @@ -0,0 +1,300 @@ +#ifndef _LGUEST_H +#define _LGUEST_H + +#include <asm/desc.h> + +#define GDT_ENTRY_LGUEST_CS 10 +#define GDT_ENTRY_LGUEST_DS 11 +#define LGUEST_CS (GDT_ENTRY_LGUEST_CS * 8) +#define LGUEST_DS (GDT_ENTRY_LGUEST_DS * 8) + +#ifndef __ASSEMBLY__ +#include <linux/types.h> +#include <linux/init.h> +#include <linux/stringify.h> +#include <linux/binfmts.h> +#include <linux/futex.h> +#include <linux/lguest.h> +#include <linux/lguest_launcher.h> +#include <linux/wait.h> +#include <linux/err.h> +#include <asm/semaphore.h> +#include "irq_vectors.h" + +#define GUEST_PL 1 + +struct lguest_regs +{ + /* Manually saved part. */ + unsigned long ebx, ecx, edx; + unsigned long esi, edi, ebp; + unsigned long gs; + unsigned long eax; + unsigned long fs, ds, es; + unsigned long trapnum, errcode; + /* Trap pushed part */ + unsigned long eip; + unsigned long cs; + unsigned long eflags; + unsigned long esp; + unsigned long ss; +}; + +void free_pagetables(void); +int init_pagetables(struct page **switcher_page, unsigned int pages); + +/* Full 4G segment descriptors, suitable for CS and DS. */ +#define FULL_EXEC_SEGMENT ((struct desc_struct){0x0000ffff, 0x00cf9b00}) +#define FULL_SEGMENT ((struct desc_struct){0x0000ffff, 0x00cf9300}) + +struct lguest_dma_info +{ + struct list_head list; + union futex_key key; + unsigned long dmas; + u16 next_dma; + u16 num_dmas; + u16 guestid; + u8 interrupt; /* 0 when not registered */ +}; + +/*H:310 The page-table code owes a great debt of gratitude to Andi Kleen. He + * reviewed the original code which used "u32" for all page table entries, and + * insisted that it would be far clearer with explicit typing. I thought it + * was overkill, but he was right: it is much clearer than it was before. + * + * We have separate types for the Guest's ptes & pgds and the shadow ptes & + * pgds. There's already a Linux type for these (pte_t and pgd_t) but they + * change depending on kernel config options (PAE). */ + +/* Each entry is identical: lower 12 bits of flags and upper 20 bits for the + * "page frame number" (0 == first physical page, etc). They are different + * types so the compiler will warn us if we mix them improperly. */ +typedef union { + struct { unsigned flags:12, pfn:20; }; + struct { unsigned long val; } raw; +} spgd_t; +typedef union { + struct { unsigned flags:12, pfn:20; }; + struct { unsigned long val; } raw; +} spte_t; +typedef union { + struct { unsigned flags:12, pfn:20; }; + struct { unsigned long val; } raw; +} gpgd_t; +typedef union { + struct { unsigned flags:12, pfn:20; }; + struct { unsigned long val; } raw; +} gpte_t; + +/* We have two convenient macros to convert a "raw" value as handed to us by + * the Guest into the correct Guest PGD or PTE type. */ +#define mkgpte(_val) ((gpte_t){.raw.val = _val}) +#define mkgpgd(_val) ((gpgd_t){.raw.val = _val}) +/*:*/ + +struct pgdir +{ + unsigned long cr3; + spgd_t *pgdir; +}; + +/* This is a guest-specific page (mapped ro) into the guest. */ +struct lguest_ro_state +{ + /* Host information we need to restore when we switch back. */ + u32 host_cr3; + struct Xgt_desc_struct host_idt_desc; + struct Xgt_desc_struct host_gdt_desc; + u32 host_sp; + + /* Fields which are used when guest is running. */ + struct Xgt_desc_struct guest_idt_desc; + struct Xgt_desc_struct guest_gdt_desc; + struct i386_hw_tss guest_tss; + struct desc_struct guest_idt[IDT_ENTRIES]; + struct desc_struct guest_gdt[GDT_ENTRIES]; +}; + +/* We have two pages shared with guests, per cpu. */ +struct lguest_pages +{ + /* This is the stack page mapped rw in guest */ + char spare[PAGE_SIZE - sizeof(struct lguest_regs)]; + struct lguest_regs regs; + + /* This is the host state & guest descriptor page, ro in guest */ + struct lguest_ro_state state; +} __attribute__((aligned(PAGE_SIZE))); + +#define CHANGED_IDT 1 +#define CHANGED_GDT 2 +#define CHANGED_GDT_TLS 4 /* Actually a subset of CHANGED_GDT */ +#define CHANGED_ALL 3 + +/* The private info the thread maintains about the guest. */ +struct lguest +{ + /* At end of a page shared mapped over lguest_pages in guest. */ + unsigned long regs_page; + struct lguest_regs *regs; + struct lguest_data __user *lguest_data; + struct task_struct *tsk; + struct mm_struct *mm; /* == tsk->mm, but that becomes NULL on exit */ + u16 guestid; + u32 pfn_limit; + u32 page_offset; + u32 cr2; + int halted; + int ts; + u32 next_hcall; + u32 esp1; + u8 ss1; + + /* Do we need to stop what we're doing and return to userspace? */ + int break_out; + wait_queue_head_t break_wq; + + /* Bitmap of what has changed: see CHANGED_* above. */ + int changed; + struct lguest_pages *last_pages; + + /* We keep a small number of these. */ + u32 pgdidx; + struct pgdir pgdirs[4]; + + /* Cached wakeup: we hold a reference to this task. */ + struct task_struct *wake; + + unsigned long noirq_start, noirq_end; + int dma_is_pending; + unsigned long pending_dma; /* struct lguest_dma */ + unsigned long pending_key; /* address they're sending to */ + + unsigned int stack_pages; + u32 tsc_khz; + + struct lguest_dma_info dma[LGUEST_MAX_DMA]; + + /* Dead? */ + const char *dead; + + /* The GDT entries copied into lguest_ro_state when running. */ + struct desc_struct gdt[GDT_ENTRIES]; + + /* The IDT entries: some copied into lguest_ro_state when running. */ + struct desc_struct idt[FIRST_EXTERNAL_VECTOR+LGUEST_IRQS]; + struct desc_struct syscall_idt; + + /* Virtual clock device */ + struct hrtimer hrt; + + /* Pending virtual interrupts */ + DECLARE_BITMAP(irqs_pending, LGUEST_IRQS); +}; + +extern struct lguest lguests[]; +extern struct mutex lguest_lock; + +/* core.c: */ +u32 lgread_u32(struct lguest *lg, unsigned long addr); +void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val); +void lgread(struct lguest *lg, void *buf, unsigned long addr, unsigned len); +void lgwrite(struct lguest *lg, unsigned long, const void *buf, unsigned len); +int find_free_guest(void); +int lguest_address_ok(const struct lguest *lg, + unsigned long addr, unsigned long len); +int run_guest(struct lguest *lg, unsigned long __user *user); + + +/* interrupts_and_traps.c: */ +void maybe_do_interrupt(struct lguest *lg); +int deliver_trap(struct lguest *lg, unsigned int num); +void load_guest_idt_entry(struct lguest *lg, unsigned int i, u32 low, u32 hi); +void guest_set_stack(struct lguest *lg, u32 seg, u32 esp, unsigned int pages); +void pin_stack_pages(struct lguest *lg); +void setup_default_idt_entries(struct lguest_ro_state *state, + const unsigned long *def); +void copy_traps(const struct lguest *lg, struct desc_struct *idt, + const unsigned long *def); +void guest_set_clockevent(struct lguest *lg, unsigned long delta); +void init_clockdev(struct lguest *lg); + +/* segments.c: */ +void setup_default_gdt_entries(struct lguest_ro_state *state); +void setup_guest_gdt(struct lguest *lg); +void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num); +void guest_load_tls(struct lguest *lg, unsigned long tls_array); +void copy_gdt(const struct lguest *lg, struct desc_struct *gdt); +void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt); + +/* page_tables.c: */ +int init_guest_pagetable(struct lguest *lg, unsigned long pgtable); +void free_guest_pagetable(struct lguest *lg); +void guest_new_pagetable(struct lguest *lg, unsigned long pgtable); +void guest_set_pmd(struct lguest *lg, unsigned long cr3, u32 i); +void guest_pagetable_clear_all(struct lguest *lg); +void guest_pagetable_flush_user(struct lguest *lg); +void guest_set_pte(struct lguest *lg, unsigned long cr3, + unsigned long vaddr, gpte_t val); +void map_switcher_in_guest(struct lguest *lg, struct lguest_pages *pages); +int demand_page(struct lguest *info, unsigned long cr2, int errcode); +void pin_page(struct lguest *lg, unsigned long vaddr); + +/* lguest_user.c: */ +int lguest_device_init(void); +void lguest_device_remove(void); + +/* io.c: */ +void lguest_io_init(void); +int bind_dma(struct lguest *lg, + unsigned long key, unsigned long udma, u16 numdmas, u8 interrupt); +void send_dma(struct lguest *info, unsigned long key, unsigned long udma); +void release_all_dma(struct lguest *lg); +unsigned long get_dma_buffer(struct lguest *lg, unsigned long key, + unsigned long *interrupt); + +/* hypercalls.c: */ +void do_hypercalls(struct lguest *lg); +void write_timestamp(struct lguest *lg); + +/*L:035 + * Let's step aside for the moment, to study one important routine that's used + * widely in the Host code. + * + * There are many cases where the Guest does something invalid, like pass crap + * to a hypercall. Since only the Guest kernel can make hypercalls, it's quite + * acceptable to simply terminate the Guest and give the Launcher a nicely + * formatted reason. It's also simpler for the Guest itself, which doesn't + * need to check most hypercalls for "success"; if you're still running, it + * succeeded. + * + * Once this is called, the Guest will never run again, so most Host code can + * call this then continue as if nothing had happened. This means many + * functions don't have to explicitly return an error code, which keeps the + * code simple. + * + * It also means that this can be called more than once: only the first one is + * remembered. The only trick is that we still need to kill the Guest even if + * we can't allocate memory to store the reason. Linux has a neat way of + * packing error codes into invalid pointers, so we use that here. + * + * Like any macro which uses an "if", it is safely wrapped in a run-once "do { + * } while(0)". + */ +#define kill_guest(lg, fmt...) \ +do { \ + if (!(lg)->dead) { \ + (lg)->dead = kasprintf(GFP_ATOMIC, fmt); \ + if (!(lg)->dead) \ + (lg)->dead = ERR_PTR(-ENOMEM); \ + } \ +} while(0) +/* (End of aside) :*/ + +static inline unsigned long guest_pa(struct lguest *lg, unsigned long vaddr) +{ + return vaddr - lg->page_offset; +} +#endif /* __ASSEMBLY__ */ +#endif /* _LGUEST_H */ diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c new file mode 100644 index 00000000000..ee1c6d05c3d --- /dev/null +++ b/drivers/lguest/lguest.c @@ -0,0 +1,1102 @@ +/*P:010 + * A hypervisor allows multiple Operating Systems to run on a single machine. + * To quote David Wheeler: "Any problem in computer science can be solved with + * another layer of indirection." + * + * We keep things simple in two ways. First, we start with a normal Linux + * kernel and insert a module (lg.ko) which allows us to run other Linux + * kernels the same way we'd run processes. We call the first kernel the Host, + * and the others the Guests. The program which sets up and configures Guests + * (such as the example in Documentation/lguest/lguest.c) is called the + * Launcher. + * + * Secondly, we only run specially modified Guests, not normal kernels. When + * you set CONFIG_LGUEST to 'y' or 'm', this automatically sets + * CONFIG_LGUEST_GUEST=y, which compiles this file into the kernel so it knows + * how to be a Guest. This means that you can use the same kernel you boot + * normally (ie. as a Host) as a Guest. + * + * These Guests know that they cannot do privileged operations, such as disable + * interrupts, and that they have to ask the Host to do such things explicitly. + * This file consists of all the replacements for such low-level native + * hardware operations: these special Guest versions call the Host. + * + * So how does the kernel know it's a Guest? The Guest starts at a special + * entry point marked with a magic string, which sets up a few things then + * calls here. We replace the native functions in "struct paravirt_ops" + * with our Guest versions, then boot like normal. :*/ + +/* + * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or + * NON INFRINGEMENT. See the GNU General Public License for more + * details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ +#include <linux/kernel.h> +#include <linux/start_kernel.h> +#include <linux/string.h> +#include <linux/console.h> +#include <linux/screen_info.h> +#include <linux/irq.h> +#include <linux/interrupt.h> +#include <linux/clocksource.h> +#include <linux/clockchips.h> +#include <linux/lguest.h> +#include <linux/lguest_launcher.h> +#include <linux/lguest_bus.h> +#include <asm/paravirt.h> +#include <asm/param.h> +#include <asm/page.h> +#include <asm/pgtable.h> +#include <asm/desc.h> +#include <asm/setup.h> +#include <asm/e820.h> +#include <asm/mce.h> +#include <asm/io.h> + +/*G:010 Welcome to the Guest! + * + * The Guest in our tale is a simple creature: identical to the Host but + * behaving in simplified but equivalent ways. In particular, the Guest is the + * same kernel as the Host (or at least, built from the same source code). :*/ + +/* Declarations for definitions in lguest_guest.S */ +extern char lguest_noirq_start[], lguest_noirq_end[]; +extern const char lgstart_cli[], lgend_cli[]; +extern const char lgstart_sti[], lgend_sti[]; +extern const char lgstart_popf[], lgend_popf[]; +extern const char lgstart_pushf[], lgend_pushf[]; +extern const char lgstart_iret[], lgend_iret[]; +extern void lguest_iret(void); + +struct lguest_data lguest_data = { + .hcall_status = { [0 ... LHCALL_RING_SIZE-1] = 0xFF }, + .noirq_start = (u32)lguest_noirq_start, + .noirq_end = (u32)lguest_noirq_end, + .blocked_interrupts = { 1 }, /* Block timer interrupts */ +}; +struct lguest_device_desc *lguest_devices; +static cycle_t clock_base; + +/*G:035 Notice the lazy_hcall() above, rather than hcall(). This is our first + * real optimization trick! + * + * When lazy_mode is set, it means we're allowed to defer all hypercalls and do + * them as a batch when lazy_mode is eventually turned off. Because hypercalls + * are reasonably expensive, batching them up makes sense. For example, a + * large mmap might update dozens of page table entries: that code calls + * lguest_lazy_mode(PARAVIRT_LAZY_MMU), does the dozen updates, then calls + * lguest_lazy_mode(PARAVIRT_LAZY_NONE). + * + * So, when we're in lazy mode, we call async_hypercall() to store the call for + * future processing. When lazy mode is turned off we issue a hypercall to + * flush the stored calls. + * + * There's also a hack where "mode" is set to "PARAVIRT_LAZY_FLUSH" which + * indicates we're to flush any outstanding calls immediately. This is used + * when an interrupt handler does a kmap_atomic(): the page table changes must + * happen immediately even if we're in the middle of a batch. Usually we're + * not, though, so there's nothing to do. */ +static enum paravirt_lazy_mode lazy_mode; /* Note: not SMP-safe! */ +static void lguest_lazy_mode(enum paravirt_lazy_mode mode) +{ + if (mode == PARAVIRT_LAZY_FLUSH) { + if (unlikely(lazy_mode != PARAVIRT_LAZY_NONE)) + hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0); + } else { + lazy_mode = mode; + if (mode == PARAVIRT_LAZY_NONE) + hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0); + } +} + +static void lazy_hcall(unsigned long call, + unsigned long arg1, + unsigned long arg2, + unsigned long arg3) +{ + if (lazy_mode == PARAVIRT_LAZY_NONE) + hcall(call, arg1, arg2, arg3); + else + async_hcall(call, arg1, arg2, arg3); +} + +/* async_hcall() is pretty simple: I'm quite proud of it really. We have a + * ring buffer of stored hypercalls which the Host will run though next time we + * do a normal hypercall. Each entry in the ring has 4 slots for the hypercall + * arguments, and a "hcall_status" word which is 0 if the call is ready to go, + * and 255 once the Host has finished with it. + * + * If we come around to a slot which hasn't been finished, then the table is + * full and we just make the hypercall directly. This has the nice side + * effect of causing the Host to run all the stored calls in the ring buffer + * which empties it for next time! */ +void async_hcall(unsigned long call, + unsigned long arg1, unsigned long arg2, unsigned long arg3) +{ + /* Note: This code assumes we're uniprocessor. */ + static unsigned int next_call; + unsigned long flags; + + /* Disable interrupts if not already disabled: we don't want an + * interrupt handler making a hypercall while we're already doing + * one! */ + local_irq_save(flags); + if (lguest_data.hcall_status[next_call] != 0xFF) { + /* Table full, so do normal hcall which will flush table. */ + hcall(call, arg1, arg2, arg3); + } else { + lguest_data.hcalls[next_call].eax = call; + lguest_data.hcalls[next_call].edx = arg1; + lguest_data.hcalls[next_call].ebx = arg2; + lguest_data.hcalls[next_call].ecx = arg3; + /* Arguments must all be written before we mark it to go */ + wmb(); + lguest_data.hcall_status[next_call] = 0; + if (++next_call == LHCALL_RING_SIZE) + next_call = 0; + } + local_irq_restore(flags); +} +/*:*/ + +/* Wrappers for the SEND_DMA and BIND_DMA hypercalls. This is mainly because + * Jeff Garzik complained that __pa() should never appear in drivers, and this + * helps remove most of them. But also, it wraps some ugliness. */ +void lguest_send_dma(unsigned long key, struct lguest_dma *dma) +{ + /* The hcall might not write this if something goes wrong */ + dma->used_len = 0; + hcall(LHCALL_SEND_DMA, key, __pa(dma), 0); +} + +int lguest_bind_dma(unsigned long key, struct lguest_dma *dmas, + unsigned int num, u8 irq) +{ + /* This is the only hypercall which actually wants 5 arguments, and we + * only support 4. Fortunately the interrupt number is always less + * than 256, so we can pack it with the number of dmas in the final + * argument. */ + if (!hcall(LHCALL_BIND_DMA, key, __pa(dmas), (num << 8) | irq)) + return -ENOMEM; + return 0; +} + +/* Unbinding is the same hypercall as binding, but with 0 num & irq. */ +void lguest_unbind_dma(unsigned long key, struct lguest_dma *dmas) +{ + hcall(LHCALL_BIND_DMA, key, __pa(dmas), 0); +} + +/* For guests, device memory can be used as normal memory, so we cast away the + * __iomem to quieten sparse. */ +void *lguest_map(unsigned long phys_addr, unsigned long pages) +{ + return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages); +} + +void lguest_unmap(void *addr) +{ + iounmap((__force void __iomem *)addr); +} + +/*G:033 + * Here are our first native-instruction replacements: four functions for + * interrupt control. + * + * The simplest way of implementing these would be to have "turn interrupts + * off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow: + * these are by far the most commonly called functions of those we override. + * + * So instead we keep an "irq_enabled" field inside our "struct lguest_data", + * which the Guest can update with a single instruction. The Host knows to + * check there when it wants to deliver an interrupt. + */ + +/* save_flags() is expected to return the processor state (ie. "eflags"). The + * eflags word contains all kind of stuff, but in practice Linux only cares + * about the interrupt flag. Our "save_flags()" just returns that. */ +static unsigned long save_fl(void) +{ + return lguest_data.irq_enabled; +} + +/* "restore_flags" just sets the flags back to the value given. */ +static void restore_fl(unsigned long flags) +{ + lguest_data.irq_enabled = flags; +} + +/* Interrupts go off... */ +static void irq_disable(void) +{ + lguest_data.irq_enabled = 0; +} + +/* Interrupts go on... */ +static void irq_enable(void) +{ + lguest_data.irq_enabled = X86_EFLAGS_IF; +} +/*:*/ +/*M:003 Note that we don't check for outstanding interrupts when we re-enable + * them (or when we unmask an interrupt). This seems to work for the moment, + * since interrupts are rare and we'll just get the interrupt on the next timer + * tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way + * would be to put the "irq_enabled" field in a page by itself, and have the + * Host write-protect it when an interrupt comes in when irqs are disabled. + * There will then be a page fault as soon as interrupts are re-enabled. :*/ + +/*G:034 + * The Interrupt Descriptor Table (IDT). + * + * The IDT tells the processor what to do when an interrupt comes in. Each + * entry in the table is a 64-bit descriptor: this holds the privilege level, + * address of the handler, and... well, who cares? The Guest just asks the + * Host to make the change anyway, because the Host controls the real IDT. + */ +static void lguest_write_idt_entry(struct desc_struct *dt, + int entrynum, u32 low, u32 high) +{ + /* Keep the local copy up to date. */ + write_dt_entry(dt, entrynum, low, high); + /* Tell Host about this new entry. */ + hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, low, high); +} + +/* Changing to a different IDT is very rare: we keep the IDT up-to-date every + * time it is written, so we can simply loop through all entries and tell the + * Host about them. */ +static void lguest_load_idt(const struct Xgt_desc_struct *desc) +{ + unsigned int i; + struct desc_struct *idt = (void *)desc->address; + + for (i = 0; i < (desc->size+1)/8; i++) + hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b); +} + +/* + * The Global Descriptor Table. + * + * The Intel architecture defines another table, called the Global Descriptor + * Table (GDT). You tell the CPU where it is (and its size) using the "lgdt" + * instruction, and then several other instructions refer to entries in the + * table. There are three entries which the Switcher needs, so the Host simply + * controls the entire thing and the Guest asks it to make changes using the + * LOAD_GDT hypercall. + * + * This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY + * hypercall and use that repeatedly to load a new IDT. I don't think it + * really matters, but wouldn't it be nice if they were the same? + */ +static void lguest_load_gdt(const struct Xgt_desc_struct *desc) +{ + BUG_ON((desc->size+1)/8 != GDT_ENTRIES); + hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0); +} + +/* For a single GDT entry which changes, we do the lazy thing: alter our GDT, + * then tell the Host to reload the entire thing. This operation is so rare + * that this naive implementation is reasonable. */ +static void lguest_write_gdt_entry(struct desc_struct *dt, + int entrynum, u32 low, u32 high) +{ + write_dt_entry(dt, entrynum, low, high); + hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0); +} + +/* OK, I lied. There are three "thread local storage" GDT entries which change + * on every context switch (these three entries are how glibc implements + * __thread variables). So we have a hypercall specifically for this case. */ +static void lguest_load_tls(struct thread_struct *t, unsigned int cpu) +{ + /* There's one problem which normal hardware doesn't have: the Host + * can't handle us removing entries we're currently using. So we clear + * the GS register here: if it's needed it'll be reloaded anyway. */ + loadsegment(gs, 0); + lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0); +} + +/*G:038 That's enough excitement for now, back to ploughing through each of + * the paravirt_ops (we're about 1/3 of the way through). + * + * This is the Local Descriptor Table, another weird Intel thingy. Linux only + * uses this for some strange applications like Wine. We don't do anything + * here, so they'll get an informative and friendly Segmentation Fault. */ +static void lguest_set_ldt(const void *addr, unsigned entries) +{ +} + +/* This loads a GDT entry into the "Task Register": that entry points to a + * structure called the Task State Segment. Some comments scattered though the + * kernel code indicate that this used for task switching in ages past, along + * with blood sacrifice and astrology. + * + * Now there's nothing interesting in here that we don't get told elsewhere. + * But the native version uses the "ltr" instruction, which makes the Host + * complain to the Guest about a Segmentation Fault and it'll oops. So we + * override the native version with a do-nothing version. */ +static void lguest_load_tr_desc(void) +{ +} + +/* The "cpuid" instruction is a way of querying both the CPU identity + * (manufacturer, model, etc) and its features. It was introduced before the + * Pentium in 1993 and keeps getting extended by both Intel and AMD. As you + * might imagine, after a decade and a half this treatment, it is now a giant + * ball of hair. Its entry in the current Intel manual runs to 28 pages. + * + * This instruction even it has its own Wikipedia entry. The Wikipedia entry + * has been translated into 4 languages. I am not making this up! + * + * We could get funky here and identify ourselves as "GenuineLguest", but + * instead we just use the real "cpuid" instruction. Then I pretty much turned + * off feature bits until the Guest booted. (Don't say that: you'll damage + * lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is + * hardly future proof.) Noone's listening! They don't like you anyway, + * parenthetic weirdo! + * + * Replacing the cpuid so we can turn features off is great for the kernel, but + * anyone (including userspace) can just use the raw "cpuid" instruction and + * the Host won't even notice since it isn't privileged. So we try not to get + * too worked up about it. */ +static void lguest_cpuid(unsigned int *eax, unsigned int *ebx, + unsigned int *ecx, unsigned int *edx) +{ + int function = *eax; + + native_cpuid(eax, ebx, ecx, edx); + switch (function) { + case 1: /* Basic feature request. */ + /* We only allow kernel to see SSE3, CMPXCHG16B and SSSE3 */ + *ecx &= 0x00002201; + /* SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, FPU. */ + *edx &= 0x07808101; + /* The Host can do a nice optimization if it knows that the + * kernel mappings (addresses above 0xC0000000 or whatever + * PAGE_OFFSET is set to) haven't changed. But Linux calls + * flush_tlb_user() for both user and kernel mappings unless + * the Page Global Enable (PGE) feature bit is set. */ + *edx |= 0x00002000; + break; + case 0x80000000: + /* Futureproof this a little: if they ask how much extended + * processor information there is, limit it to known fields. */ + if (*eax > 0x80000008) + *eax = 0x80000008; + break; + } +} + +/* Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4. + * I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother + * it. The Host needs to know when the Guest wants to change them, so we have + * a whole series of functions like read_cr0() and write_cr0(). + * + * We start with CR0. CR0 allows you to turn on and off all kinds of basic + * features, but Linux only really cares about one: the horrifically-named Task + * Switched (TS) bit at bit 3 (ie. 8) + * + * What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if + * the floating point unit is used. Which allows us to restore FPU state + * lazily after a task switch, and Linux uses that gratefully, but wouldn't a + * name like "FPUTRAP bit" be a little less cryptic? + * + * We store cr0 (and cr3) locally, because the Host never changes it. The + * Guest sometimes wants to read it and we'd prefer not to bother the Host + * unnecessarily. */ +static unsigned long current_cr0, current_cr3; +static void lguest_write_cr0(unsigned long val) +{ + /* 8 == TS bit. */ + lazy_hcall(LHCALL_TS, val & 8, 0, 0); + current_cr0 = val; +} + +static unsigned long lguest_read_cr0(void) +{ + return current_cr0; +} + +/* Intel provided a special instruction to clear the TS bit for people too cool + * to use write_cr0() to do it. This "clts" instruction is faster, because all + * the vowels have been optimized out. */ +static void lguest_clts(void) +{ + lazy_hcall(LHCALL_TS, 0, 0, 0); + current_cr0 &= ~8U; +} + +/* CR2 is the virtual address of the last page fault, which the Guest only ever + * reads. The Host kindly writes this into our "struct lguest_data", so we + * just read it out of there. */ +static unsigned long lguest_read_cr2(void) +{ + return lguest_data.cr2; +} + +/* CR3 is the current toplevel pagetable page: the principle is the same as + * cr0. Keep a local copy, and tell the Host when it changes. */ +static void lguest_write_cr3(unsigned long cr3) +{ + lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0); + current_cr3 = cr3; +} + +static unsigned long lguest_read_cr3(void) +{ + return current_cr3; +} + +/* CR4 is used to enable and disable PGE, but we don't care. */ +static unsigned long lguest_read_cr4(void) +{ + return 0; +} + +static void lguest_write_cr4(unsigned long val) +{ +} + +/* + * Page Table Handling. + * + * Now would be a good time to take a rest and grab a coffee or similarly + * relaxing stimulant. The easy parts are behind us, and the trek gradually + * winds uphill from here. + * + * Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU + * maps virtual addresses to physical addresses using "page tables". We could + * use one huge index of 1 million entries: each address is 4 bytes, so that's + * 1024 pages just to hold the page tables. But since most virtual addresses + * are unused, we use a two level index which saves space. The CR3 register + * contains the physical address of the top level "page directory" page, which + * contains physical addresses of up to 1024 second-level pages. Each of these + * second level pages contains up to 1024 physical addresses of actual pages, + * or Page Table Entries (PTEs). + * + * Here's a diagram, where arrows indicate physical addresses: + * + * CR3 ---> +---------+ + * | --------->+---------+ + * | | | PADDR1 | + * Top-level | | PADDR2 | + * (PMD) page | | | + * | | Lower-level | + * | | (PTE) page | + * | | | | + * .... .... + * + * So to convert a virtual address to a physical address, we look up the top + * level, which points us to the second level, which gives us the physical + * address of that page. If the top level entry was not present, or the second + * level entry was not present, then the virtual address is invalid (we + * say "the page was not mapped"). + * + * Put another way, a 32-bit virtual address is divided up like so: + * + * 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 + * |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>| + * Index into top Index into second Offset within page + * page directory page pagetable page + * + * The kernel spends a lot of time changing both the top-level page directory + * and lower-level pagetable pages. The Guest doesn't know physical addresses, + * so while it maintains these page tables exactly like normal, it also needs + * to keep the Host informed whenever it makes a change: the Host will create + * the real page tables based on the Guests'. + */ + +/* The Guest calls this to set a second-level entry (pte), ie. to map a page + * into a process' address space. We set the entry then tell the Host the + * toplevel and address this corresponds to. The Guest uses one pagetable per + * process, so we need to tell the Host which one we're changing (mm->pgd). */ +static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pteval) +{ + *ptep = pteval; + lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, pteval.pte_low); +} + +/* The Guest calls this to set a top-level entry. Again, we set the entry then + * tell the Host which top-level page we changed, and the index of the entry we + * changed. */ +static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval) +{ + *pmdp = pmdval; + lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK, + (__pa(pmdp)&(PAGE_SIZE-1))/4, 0); +} + +/* There are a couple of legacy places where the kernel sets a PTE, but we + * don't know the top level any more. This is useless for us, since we don't + * know which pagetable is changing or what address, so we just tell the Host + * to forget all of them. Fortunately, this is very rare. + * + * ... except in early boot when the kernel sets up the initial pagetables, + * which makes booting astonishingly slow. So we don't even tell the Host + * anything changed until we've done the first page table switch. + */ +static void lguest_set_pte(pte_t *ptep, pte_t pteval) +{ + *ptep = pteval; + /* Don't bother with hypercall before initial setup. */ + if (current_cr3) + lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0); +} + +/* Unfortunately for Lguest, the paravirt_ops for page tables were based on + * native page table operations. On native hardware you can set a new page + * table entry whenever you want, but if you want to remove one you have to do + * a TLB flush (a TLB is a little cache of page table entries kept by the CPU). + * + * So the lguest_set_pte_at() and lguest_set_pmd() functions above are only + * called when a valid entry is written, not when it's removed (ie. marked not + * present). Instead, this is where we come when the Guest wants to remove a + * page table entry: we tell the Host to set that entry to 0 (ie. the present + * bit is zero). */ +static void lguest_flush_tlb_single(unsigned long addr) +{ + /* Simply set it to zero: if it was not, it will fault back in. */ + lazy_hcall(LHCALL_SET_PTE, current_cr3, addr, 0); +} + +/* This is what happens after the Guest has removed a large number of entries. + * This tells the Host that any of the page table entries for userspace might + * have changed, ie. virtual addresses below PAGE_OFFSET. */ +static void lguest_flush_tlb_user(void) +{ + lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0); +} + +/* This is called when the kernel page tables have changed. That's not very + * common (unless the Guest is using highmem, which makes the Guest extremely + * slow), so it's worth separating this from the user flushing above. */ +static void lguest_flush_tlb_kernel(void) +{ + lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0); +} + +/* + * The Unadvanced Programmable Interrupt Controller. + * + * This is an attempt to implement the simplest possible interrupt controller. + * I spent some time looking though routines like set_irq_chip_and_handler, + * set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and + * I *think* this is as simple as it gets. + * + * We can tell the Host what interrupts we want blocked ready for using the + * lguest_data.interrupts bitmap, so disabling (aka "masking") them is as + * simple as setting a bit. We don't actually "ack" interrupts as such, we + * just mask and unmask them. I wonder if we should be cleverer? + */ +static void disable_lguest_irq(unsigned int irq) +{ + set_bit(irq, lguest_data.blocked_interrupts); +} + +static void enable_lguest_irq(unsigned int irq) +{ + clear_bit(irq, lguest_data.blocked_interrupts); +} + +/* This structure describes the lguest IRQ controller. */ +static struct irq_chip lguest_irq_controller = { + .name = "lguest", + .mask = disable_lguest_irq, + .mask_ack = disable_lguest_irq, + .unmask = enable_lguest_irq, +}; + +/* This sets up the Interrupt Descriptor Table (IDT) entry for each hardware + * interrupt (except 128, which is used for system calls), and then tells the + * Linux infrastructure that each interrupt is controlled by our level-based + * lguest interrupt controller. */ +static void __init lguest_init_IRQ(void) +{ + unsigned int i; + + for (i = 0; i < LGUEST_IRQS; i++) { + int vector = FIRST_EXTERNAL_VECTOR + i; + if (vector != SYSCALL_VECTOR) { + set_intr_gate(vector, interrupt[i]); + set_irq_chip_and_handler(i, &lguest_irq_controller, + handle_level_irq); + } + } + /* This call is required to set up for 4k stacks, where we have + * separate stacks for hard and soft interrupts. */ + irq_ctx_init(smp_processor_id()); +} + +/* + * Time. + * + * It would be far better for everyone if the Guest had its own clock, but + * until then the Host gives us the time on every interrupt. + */ +static unsigned long lguest_get_wallclock(void) +{ + return lguest_data.time.tv_sec; +} + +static cycle_t lguest_clock_read(void) +{ + unsigned long sec, nsec; + + /* If the Host tells the TSC speed, we can trust that. */ + if (lguest_data.tsc_khz) + return native_read_tsc(); + + /* If we can't use the TSC, we read the time value written by the Host. + * Since it's in two parts (seconds and nanoseconds), we risk reading + * it just as it's changing from 99 & 0.999999999 to 100 and 0, and + * getting 99 and 0. As Linux tends to come apart under the stress of + * time travel, we must be careful: */ + do { + /* First we read the seconds part. */ + sec = lguest_data.time.tv_sec; + /* This read memory barrier tells the compiler and the CPU that + * this can't be reordered: we have to complete the above + * before going on. */ + rmb(); + /* Now we read the nanoseconds part. */ + nsec = lguest_data.time.tv_nsec; + /* Make sure we've done that. */ + rmb(); + /* Now if the seconds part has changed, try again. */ + } while (unlikely(lguest_data.time.tv_sec != sec)); + + /* Our non-TSC clock is in real nanoseconds. */ + return sec*1000000000ULL + nsec; +} + +/* This is what we tell the kernel is our clocksource. */ +static struct clocksource lguest_clock = { + .name = "lguest", + .rating = 400, + .read = lguest_clock_read, + .mask = CLOCKSOURCE_MASK(64), + .mult = 1 << 22, + .shift = 22, +}; + +/* The "scheduler clock" is just our real clock, adjusted to start at zero */ +static unsigned long long lguest_sched_clock(void) +{ + return cyc2ns(&lguest_clock, lguest_clock_read() - clock_base); +} + +/* We also need a "struct clock_event_device": Linux asks us to set it to go + * off some time in the future. Actually, James Morris figured all this out, I + * just applied the patch. */ +static int lguest_clockevent_set_next_event(unsigned long delta, + struct clock_event_device *evt) +{ + if (delta < LG_CLOCK_MIN_DELTA) { + if (printk_ratelimit()) + printk(KERN_DEBUG "%s: small delta %lu ns\n", + __FUNCTION__, delta); + return -ETIME; + } + hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0); + return 0; +} + +static void lguest_clockevent_set_mode(enum clock_event_mode mode, + struct clock_event_device *evt) +{ + switch (mode) { + case CLOCK_EVT_MODE_UNUSED: + case CLOCK_EVT_MODE_SHUTDOWN: + /* A 0 argument shuts the clock down. */ + hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0); + break; + case CLOCK_EVT_MODE_ONESHOT: + /* This is what we expect. */ + break; + case CLOCK_EVT_MODE_PERIODIC: + BUG(); + case CLOCK_EVT_MODE_RESUME: + break; + } +} + +/* This describes our primitive timer chip. */ +static struct clock_event_device lguest_clockevent = { + .name = "lguest", + .features = CLOCK_EVT_FEAT_ONESHOT, + .set_next_event = lguest_clockevent_set_next_event, + .set_mode = lguest_clockevent_set_mode, + .rating = INT_MAX, + .mult = 1, + .shift = 0, + .min_delta_ns = LG_CLOCK_MIN_DELTA, + .max_delta_ns = LG_CLOCK_MAX_DELTA, +}; + +/* This is the Guest timer interrupt handler (hardware interrupt 0). We just + * call the clockevent infrastructure and it does whatever needs doing. */ +static void lguest_time_irq(unsigned int irq, struct irq_desc *desc) +{ + unsigned long flags; + + /* Don't interrupt us while this is running. */ + local_irq_save(flags); + lguest_clockevent.event_handler(&lguest_clockevent); + local_irq_restore(flags); +} + +/* At some point in the boot process, we get asked to set up our timing + * infrastructure. The kernel doesn't expect timer interrupts before this, but + * we cleverly initialized the "blocked_interrupts" field of "struct + * lguest_data" so that timer interrupts were blocked until now. */ +static void lguest_time_init(void) +{ + /* Set up the timer interrupt (0) to go to our simple timer routine */ + set_irq_handler(0, lguest_time_irq); + + /* Our clock structure look like arch/i386/kernel/tsc.c if we can use + * the TSC, otherwise it's a dumb nanosecond-resolution clock. Either + * way, the "rating" is initialized so high that it's always chosen + * over any other clocksource. */ + if (lguest_data.tsc_khz) { + lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz, + lguest_clock.shift); + lguest_clock.flags = CLOCK_SOURCE_IS_CONTINUOUS; + } + clock_base = lguest_clock_read(); + clocksource_register(&lguest_clock); + + /* Now we've set up our clock, we can use it as the scheduler clock */ + paravirt_ops.sched_clock = lguest_sched_clock; + + /* We can't set cpumask in the initializer: damn C limitations! Set it + * here and register our timer device. */ + lguest_clockevent.cpumask = cpumask_of_cpu(0); + clockevents_register_device(&lguest_clockevent); + + /* Finally, we unblock the timer interrupt. */ + enable_lguest_irq(0); +} + +/* + * Miscellaneous bits and pieces. + * + * Here is an oddball collection of functions which the Guest needs for things + * to work. They're pretty simple. + */ + +/* The Guest needs to tell the host what stack it expects traps to use. For + * native hardware, this is part of the Task State Segment mentioned above in + * lguest_load_tr_desc(), but to help hypervisors there's this special call. + * + * We tell the Host the segment we want to use (__KERNEL_DS is the kernel data + * segment), the privilege level (we're privilege level 1, the Host is 0 and + * will not tolerate us trying to use that), the stack pointer, and the number + * of pages in the stack. */ +static void lguest_load_esp0(struct tss_struct *tss, + struct thread_struct *thread) +{ + lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->esp0, + THREAD_SIZE/PAGE_SIZE); +} + +/* Let's just say, I wouldn't do debugging under a Guest. */ +static void lguest_set_debugreg(int regno, unsigned long value) +{ + /* FIXME: Implement */ +} + +/* There are times when the kernel wants to make sure that no memory writes are + * caught in the cache (that they've all reached real hardware devices). This + * doesn't matter for the Guest which has virtual hardware. + * + * On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush + * (clflush) instruction is available and the kernel uses that. Otherwise, it + * uses the older "Write Back and Invalidate Cache" (wbinvd) instruction. + * Unlike clflush, wbinvd can only be run at privilege level 0. So we can + * ignore clflush, but replace wbinvd. + */ +static void lguest_wbinvd(void) +{ +} + +/* If the Guest expects to have an Advanced Programmable Interrupt Controller, + * we play dumb by ignoring writes and returning 0 for reads. So it's no + * longer Programmable nor Controlling anything, and I don't think 8 lines of + * code qualifies for Advanced. It will also never interrupt anything. It + * does, however, allow us to get through the Linux boot code. */ +#ifdef CONFIG_X86_LOCAL_APIC +static void lguest_apic_write(unsigned long reg, unsigned long v) +{ +} + +static unsigned long lguest_apic_read(unsigned long reg) +{ + return 0; +} +#endif + +/* STOP! Until an interrupt comes in. */ +static void lguest_safe_halt(void) +{ + hcall(LHCALL_HALT, 0, 0, 0); +} + +/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a + * message out when we're crashing as well as elegant termination like powering + * off. + * + * Note that the Host always prefers that the Guest speak in physical addresses + * rather than virtual addresses, so we use __pa() here. */ +static void lguest_power_off(void) +{ + hcall(LHCALL_CRASH, __pa("Power down"), 0, 0); +} + +/* + * Panicing. + * + * Don't. But if you did, this is what happens. + */ +static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p) +{ + hcall(LHCALL_CRASH, __pa(p), 0, 0); + /* The hcall won't return, but to keep gcc happy, we're "done". */ + return NOTIFY_DONE; +} + +static struct notifier_block paniced = { + .notifier_call = lguest_panic +}; + +/* Setting up memory is fairly easy. */ +static __init char *lguest_memory_setup(void) +{ + /* We do this here and not earlier because lockcheck barfs if we do it + * before start_kernel() */ + atomic_notifier_chain_register(&panic_notifier_list, &paniced); + + /* The Linux bootloader header contains an "e820" memory map: the + * Launcher populated the first entry with our memory limit. */ + add_memory_region(E820_MAP->addr, E820_MAP->size, E820_MAP->type); + + /* This string is for the boot messages. */ + return "LGUEST"; +} + +/*G:050 + * Patching (Powerfully Placating Performance Pedants) + * + * We have already seen that "struct paravirt_ops" lets us replace simple + * native instructions with calls to the appropriate back end all throughout + * the kernel. This allows the same kernel to run as a Guest and as a native + * kernel, but it's slow because of all the indirect branches. + * + * Remember that David Wheeler quote about "Any problem in computer science can + * be solved with another layer of indirection"? The rest of that quote is + * "... But that usually will create another problem." This is the first of + * those problems. + * + * Our current solution is to allow the paravirt back end to optionally patch + * over the indirect calls to replace them with something more efficient. We + * patch the four most commonly called functions: disable interrupts, enable + * interrupts, restore interrupts and save interrupts. We usually have 10 + * bytes to patch into: the Guest versions of these operations are small enough + * that we can fit comfortably. + * + * First we need assembly templates of each of the patchable Guest operations, + * and these are in lguest_asm.S. */ + +/*G:060 We construct a table from the assembler templates: */ +static const struct lguest_insns +{ + const char *start, *end; +} lguest_insns[] = { + [PARAVIRT_PATCH(irq_disable)] = { lgstart_cli, lgend_cli }, + [PARAVIRT_PATCH(irq_enable)] = { lgstart_sti, lgend_sti }, + [PARAVIRT_PATCH(restore_fl)] = { lgstart_popf, lgend_popf }, + [PARAVIRT_PATCH(save_fl)] = { lgstart_pushf, lgend_pushf }, +}; + +/* Now our patch routine is fairly simple (based on the native one in + * paravirt.c). If we have a replacement, we copy it in and return how much of + * the available space we used. */ +static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf, + unsigned long addr, unsigned len) +{ + unsigned int insn_len; + + /* Don't do anything special if we don't have a replacement */ + if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start) + return paravirt_patch_default(type, clobber, ibuf, addr, len); + + insn_len = lguest_insns[type].end - lguest_insns[type].start; + + /* Similarly if we can't fit replacement (shouldn't happen, but let's + * be thorough). */ + if (len < insn_len) + return paravirt_patch_default(type, clobber, ibuf, addr, len); + + /* Copy in our instructions. */ + memcpy(ibuf, lguest_insns[type].start, insn_len); + return insn_len; +} + +/*G:030 Once we get to lguest_init(), we know we're a Guest. The paravirt_ops + * structure in the kernel provides a single point for (almost) every routine + * we have to override to avoid privileged instructions. */ +__init void lguest_init(void *boot) +{ + /* Copy boot parameters first: the Launcher put the physical location + * in %esi, and head.S converted that to a virtual address and handed + * it to us. We use "__memcpy" because "memcpy" sometimes tries to do + * tricky things to go faster, and we're not ready for that. */ + __memcpy(&boot_params, boot, PARAM_SIZE); + /* The boot parameters also tell us where the command-line is: save + * that, too. */ + __memcpy(boot_command_line, __va(boot_params.hdr.cmd_line_ptr), + COMMAND_LINE_SIZE); + + /* We're under lguest, paravirt is enabled, and we're running at + * privilege level 1, not 0 as normal. */ + paravirt_ops.name = "lguest"; + paravirt_ops.paravirt_enabled = 1; + paravirt_ops.kernel_rpl = 1; + + /* We set up all the lguest overrides for sensitive operations. These + * are detailed with the operations themselves. */ + paravirt_ops.save_fl = save_fl; + paravirt_ops.restore_fl = restore_fl; + paravirt_ops.irq_disable = irq_disable; + paravirt_ops.irq_enable = irq_enable; + paravirt_ops.load_gdt = lguest_load_gdt; + paravirt_ops.memory_setup = lguest_memory_setup; + paravirt_ops.cpuid = lguest_cpuid; + paravirt_ops.write_cr3 = lguest_write_cr3; + paravirt_ops.flush_tlb_user = lguest_flush_tlb_user; + paravirt_ops.flush_tlb_single = lguest_flush_tlb_single; + paravirt_ops.flush_tlb_kernel = lguest_flush_tlb_kernel; + paravirt_ops.set_pte = lguest_set_pte; + paravirt_ops.set_pte_at = lguest_set_pte_at; + paravirt_ops.set_pmd = lguest_set_pmd; +#ifdef CONFIG_X86_LOCAL_APIC + paravirt_ops.apic_write = lguest_apic_write; + paravirt_ops.apic_write_atomic = lguest_apic_write; + paravirt_ops.apic_read = lguest_apic_read; +#endif + paravirt_ops.load_idt = lguest_load_idt; + paravirt_ops.iret = lguest_iret; + paravirt_ops.load_esp0 = lguest_load_esp0; + paravirt_ops.load_tr_desc = lguest_load_tr_desc; + paravirt_ops.set_ldt = lguest_set_ldt; + paravirt_ops.load_tls = lguest_load_tls; + paravirt_ops.set_debugreg = lguest_set_debugreg; + paravirt_ops.clts = lguest_clts; + paravirt_ops.read_cr0 = lguest_read_cr0; + paravirt_ops.write_cr0 = lguest_write_cr0; + paravirt_ops.init_IRQ = lguest_init_IRQ; + paravirt_ops.read_cr2 = lguest_read_cr2; + paravirt_ops.read_cr3 = lguest_read_cr3; + paravirt_ops.read_cr4 = lguest_read_cr4; + paravirt_ops.write_cr4 = lguest_write_cr4; + paravirt_ops.write_gdt_entry = lguest_write_gdt_entry; + paravirt_ops.write_idt_entry = lguest_write_idt_entry; + paravirt_ops.patch = lguest_patch; + paravirt_ops.safe_halt = lguest_safe_halt; + paravirt_ops.get_wallclock = lguest_get_wallclock; + paravirt_ops.time_init = lguest_time_init; + paravirt_ops.set_lazy_mode = lguest_lazy_mode; + paravirt_ops.wbinvd = lguest_wbinvd; + /* Now is a good time to look at the implementations of these functions + * before returning to the rest of lguest_init(). */ + + /*G:070 Now we've seen all the paravirt_ops, we return to + * lguest_init() where the rest of the fairly chaotic boot setup + * occurs. + * + * The Host expects our first hypercall to tell it where our "struct + * lguest_data" is, so we do that first. */ + hcall(LHCALL_LGUEST_INIT, __pa(&lguest_data), 0, 0); + + /* The native boot code sets up initial page tables immediately after + * the kernel itself, and sets init_pg_tables_end so they're not + * clobbered. The Launcher places our initial pagetables somewhere at + * the top of our physical memory, so we don't need extra space: set + * init_pg_tables_end to the end of the kernel. */ + init_pg_tables_end = __pa(pg0); + + /* Load the %fs segment register (the per-cpu segment register) with + * the normal data segment to get through booting. */ + asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory"); + + /* Clear the part of the kernel data which is expected to be zero. + * Normally it will be anyway, but if we're loading from a bzImage with + * CONFIG_RELOCATALE=y, the relocations will be sitting here. */ + memset(__bss_start, 0, __bss_stop - __bss_start); + + /* The Host uses the top of the Guest's virtual address space for the + * Host<->Guest Switcher, and it tells us how much it needs in + * lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */ + reserve_top_address(lguest_data.reserve_mem); + + /* If we don't initialize the lock dependency checker now, it crashes + * paravirt_disable_iospace. */ + lockdep_init(); + + /* The IDE code spends about 3 seconds probing for disks: if we reserve + * all the I/O ports up front it can't get them and so doesn't probe. + * Other device drivers are similar (but less severe). This cuts the + * kernel boot time on my machine from 4.1 seconds to 0.45 seconds. */ + paravirt_disable_iospace(); + + /* This is messy CPU setup stuff which the native boot code does before + * start_kernel, so we have to do, too: */ + cpu_detect(&new_cpu_data); + /* head.S usually sets up the first capability word, so do it here. */ + new_cpu_data.x86_capability[0] = cpuid_edx(1); + + /* Math is always hard! */ + new_cpu_data.hard_math = 1; + +#ifdef CONFIG_X86_MCE + mce_disabled = 1; +#endif +#ifdef CONFIG_ACPI + acpi_disabled = 1; + acpi_ht = 0; +#endif + + /* We set the perferred console to "hvc". This is the "hypervisor + * virtual console" driver written by the PowerPC people, which we also + * adapted for lguest's use. */ + add_preferred_console("hvc", 0, NULL); + + /* Last of all, we set the power management poweroff hook to point to + * the Guest routine to power off. */ + pm_power_off = lguest_power_off; + + /* Now we're set up, call start_kernel() in init/main.c and we proceed + * to boot as normal. It never returns. */ + start_kernel(); +} +/* + * This marks the end of stage II of our journey, The Guest. + * + * It is now time for us to explore the nooks and crannies of the three Guest + * devices and complete our understanding of the Guest in "make Drivers". + */ diff --git a/drivers/lguest/lguest_asm.S b/drivers/lguest/lguest_asm.S new file mode 100644 index 00000000000..1ddcd5cd20f --- /dev/null +++ b/drivers/lguest/lguest_asm.S @@ -0,0 +1,93 @@ +#include <linux/linkage.h> +#include <linux/lguest.h> +#include <asm/asm-offsets.h> +#include <asm/thread_info.h> +#include <asm/processor-flags.h> + +/*G:020 This is where we begin: we have a magic signature which the launcher + * looks for. The plan is that the Linux boot protocol will be extended with a + * "platform type" field which will guide us here from the normal entry point, + * but for the moment this suffices. The normal boot code uses %esi for the + * boot header, so we do too. We convert it to a virtual address by adding + * PAGE_OFFSET, and hand it to lguest_init() as its argument (ie. %eax). + * + * The .section line puts this code in .init.text so it will be discarded after + * boot. */ +.section .init.text, "ax", @progbits +.ascii "GenuineLguest" + /* Set up initial stack. */ + movl $(init_thread_union+THREAD_SIZE),%esp + movl %esi, %eax + addl $__PAGE_OFFSET, %eax + jmp lguest_init + +/*G:055 We create a macro which puts the assembler code between lgstart_ and + * lgend_ markers. These templates are put in the .text section: they can't be + * discarded after boot as we may need to patch modules, too. */ +.text +#define LGUEST_PATCH(name, insns...) \ + lgstart_##name: insns; lgend_##name:; \ + .globl lgstart_##name; .globl lgend_##name + +LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled) +LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled) +LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled) +LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax) +/*:*/ + +/* These demark the EIP range where host should never deliver interrupts. */ +.global lguest_noirq_start +.global lguest_noirq_end + +/*M:004 When the Host reflects a trap or injects an interrupt into the Guest, + * it sets the eflags interrupt bit on the stack based on + * lguest_data.irq_enabled, so the Guest iret logic does the right thing when + * restoring it. However, when the Host sets the Guest up for direct traps, + * such as system calls, the processor is the one to push eflags onto the + * stack, and the interrupt bit will be 1 (in reality, interrupts are always + * enabled in the Guest). + * + * This turns out to be harmless: the only trap which should happen under Linux + * with interrupts disabled is Page Fault (due to our lazy mapping of vmalloc + * regions), which has to be reflected through the Host anyway. If another + * trap *does* go off when interrupts are disabled, the Guest will panic, and + * we'll never get to this iret! :*/ + +/*G:045 There is one final paravirt_op that the Guest implements, and glancing + * at it you can see why I left it to last. It's *cool*! It's in *assembler*! + * + * The "iret" instruction is used to return from an interrupt or trap. The + * stack looks like this: + * old address + * old code segment & privilege level + * old processor flags ("eflags") + * + * The "iret" instruction pops those values off the stack and restores them all + * at once. The only problem is that eflags includes the Interrupt Flag which + * the Guest can't change: the CPU will simply ignore it when we do an "iret". + * So we have to copy eflags from the stack to lguest_data.irq_enabled before + * we do the "iret". + * + * There are two problems with this: firstly, we need to use a register to do + * the copy and secondly, the whole thing needs to be atomic. The first + * problem is easy to solve: push %eax on the stack so we can use it, and then + * restore it at the end just before the real "iret". + * + * The second is harder: copying eflags to lguest_data.irq_enabled will turn + * interrupts on before we're finished, so we could be interrupted before we + * return to userspace or wherever. Our solution to this is to surround the + * code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the + * Host that it is *never* to interrupt us there, even if interrupts seem to be + * enabled. */ +ENTRY(lguest_iret) + pushl %eax + movl 12(%esp), %eax +lguest_noirq_start: + /* Note the %ss: segment prefix here. Normal data accesses use the + * "ds" segment, but that will have already been restored for whatever + * we're returning to (such as userspace): we can't trust it. The %ss: + * prefix makes sure we use the stack segment, which is still valid. */ + movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled + popl %eax + iret +lguest_noirq_end: diff --git a/drivers/lguest/lguest_bus.c b/drivers/lguest/lguest_bus.c new file mode 100644 index 00000000000..9e7752cc800 --- /dev/null +++ b/drivers/lguest/lguest_bus.c @@ -0,0 +1,218 @@ +/*P:050 Lguest guests use a very simple bus for devices. It's a simple array + * of device descriptors contained just above the top of normal memory. The + * lguest bus is 80% tedious boilerplate code. :*/ +#include <linux/init.h> +#include <linux/bootmem.h> +#include <linux/lguest_bus.h> +#include <asm/io.h> +#include <asm/paravirt.h> + +static ssize_t type_show(struct device *_dev, + struct device_attribute *attr, char *buf) +{ + struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); + return sprintf(buf, "%hu", lguest_devices[dev->index].type); +} +static ssize_t features_show(struct device *_dev, + struct device_attribute *attr, char *buf) +{ + struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); + return sprintf(buf, "%hx", lguest_devices[dev->index].features); +} +static ssize_t pfn_show(struct device *_dev, + struct device_attribute *attr, char *buf) +{ + struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); + return sprintf(buf, "%u", lguest_devices[dev->index].pfn); +} +static ssize_t status_show(struct device *_dev, + struct device_attribute *attr, char *buf) +{ + struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); + return sprintf(buf, "%hx", lguest_devices[dev->index].status); +} +static ssize_t status_store(struct device *_dev, struct device_attribute *attr, + const char *buf, size_t count) +{ + struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); + if (sscanf(buf, "%hi", &lguest_devices[dev->index].status) != 1) + return -EINVAL; + return count; +} +static struct device_attribute lguest_dev_attrs[] = { + __ATTR_RO(type), + __ATTR_RO(features), + __ATTR_RO(pfn), + __ATTR(status, 0644, status_show, status_store), + __ATTR_NULL +}; + +/*D:130 The generic bus infrastructure requires a function which says whether a + * device matches a driver. For us, it is simple: "struct lguest_driver" + * contains a "device_type" field which indicates what type of device it can + * handle, so we just cast the args and compare: */ +static int lguest_dev_match(struct device *_dev, struct device_driver *_drv) +{ + struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); + struct lguest_driver *drv = container_of(_drv,struct lguest_driver,drv); + + return (drv->device_type == lguest_devices[dev->index].type); +} +/*:*/ + +struct lguest_bus { + struct bus_type bus; + struct device dev; +}; + +static struct lguest_bus lguest_bus = { + .bus = { + .name = "lguest", + .match = lguest_dev_match, + .dev_attrs = lguest_dev_attrs, + }, + .dev = { + .parent = NULL, + .bus_id = "lguest", + } +}; + +/*D:140 This is the callback which occurs once the bus infrastructure matches + * up a device and driver, ie. in response to add_lguest_device() calling + * device_register(), or register_lguest_driver() calling driver_register(). + * + * At the moment it's always the latter: the devices are added first, since + * scan_devices() is called from a "core_initcall", and the drivers themselves + * called later as a normal "initcall". But it would work the other way too. + * + * So now we have the happy couple, we add the status bit to indicate that we + * found a driver. If the driver truly loves the device, it will return + * happiness from its probe function (ok, perhaps this wasn't my greatest + * analogy), and we set the final "driver ok" bit so the Host sees it's all + * green. */ +static int lguest_dev_probe(struct device *_dev) +{ + int ret; + struct lguest_device*dev = container_of(_dev,struct lguest_device,dev); + struct lguest_driver*drv = container_of(dev->dev.driver, + struct lguest_driver, drv); + + lguest_devices[dev->index].status |= LGUEST_DEVICE_S_DRIVER; + ret = drv->probe(dev); + if (ret == 0) + lguest_devices[dev->index].status |= LGUEST_DEVICE_S_DRIVER_OK; + return ret; +} + +/* The last part of the bus infrastructure is the function lguest drivers use + * to register themselves. Firstly, we do nothing if there's no lguest bus + * (ie. this is not a Guest), otherwise we fill in the embedded generic "struct + * driver" fields and call the generic driver_register(). */ +int register_lguest_driver(struct lguest_driver *drv) +{ + if (!lguest_devices) + return 0; + + drv->drv.bus = &lguest_bus.bus; + drv->drv.name = drv->name; + drv->drv.owner = drv->owner; + drv->drv.probe = lguest_dev_probe; + + return driver_register(&drv->drv); +} + +/* At the moment we build all the drivers into the kernel because they're so + * simple: 8144 bytes for all three of them as I type this. And as the console + * really needs to be built in, it's actually only 3527 bytes for the network + * and block drivers. + * + * If they get complex it will make sense for them to be modularized, so we + * need to explicitly export the symbol. + * + * I don't think non-GPL modules make sense, so it's a GPL-only export. + */ +EXPORT_SYMBOL_GPL(register_lguest_driver); + +/*D:120 This is the core of the lguest bus: actually adding a new device. + * It's a separate function because it's neater that way, and because an + * earlier version of the code supported hotplug and unplug. They were removed + * early on because they were never used. + * + * As Andrew Tridgell says, "Untested code is buggy code". + * + * It's worth reading this carefully: we start with an index into the array of + * "struct lguest_device_desc"s indicating the device which is new: */ +static void add_lguest_device(unsigned int index) +{ + struct lguest_device *new; + + /* Each "struct lguest_device_desc" has a "status" field, which the + * Guest updates as the device is probed. In the worst case, the Host + * can look at these bits to tell what part of device setup failed, + * even if the console isn't available. */ + lguest_devices[index].status |= LGUEST_DEVICE_S_ACKNOWLEDGE; + new = kmalloc(sizeof(struct lguest_device), GFP_KERNEL); + if (!new) { + printk(KERN_EMERG "Cannot allocate lguest device %u\n", index); + lguest_devices[index].status |= LGUEST_DEVICE_S_FAILED; + return; + } + + /* The "struct lguest_device" setup is pretty straight-forward example + * code. */ + new->index = index; + new->private = NULL; + memset(&new->dev, 0, sizeof(new->dev)); + new->dev.parent = &lguest_bus.dev; + new->dev.bus = &lguest_bus.bus; + sprintf(new->dev.bus_id, "%u", index); + + /* device_register() causes the bus infrastructure to look for a + * matching driver. */ + if (device_register(&new->dev) != 0) { + printk(KERN_EMERG "Cannot register lguest device %u\n", index); + lguest_devices[index].status |= LGUEST_DEVICE_S_FAILED; + kfree(new); + } +} + +/*D:110 scan_devices() simply iterates through the device array. The type 0 + * is reserved to mean "no device", and anything else means we have found a + * device: add it. */ +static void scan_devices(void) +{ + unsigned int i; + + for (i = 0; i < LGUEST_MAX_DEVICES; i++) + if (lguest_devices[i].type) + add_lguest_device(i); +} + +/*D:100 Fairly early in boot, lguest_bus_init() is called to set up the lguest + * bus. We check that we are a Guest by checking paravirt_ops.name: there are + * other ways of checking, but this seems most obvious to me. + * + * So we can access the array of "struct lguest_device_desc"s easily, we map + * that memory and store the pointer in the global "lguest_devices". Then we + * register the bus with the core. Doing two registrations seems clunky to me, + * but it seems to be the correct sysfs incantation. + * + * Finally we call scan_devices() which adds all the devices found in the + * "struct lguest_device_desc" array. */ +static int __init lguest_bus_init(void) +{ + if (strcmp(paravirt_ops.name, "lguest") != 0) + return 0; + + /* Devices are in a single page above top of "normal" mem */ + lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1); + + if (bus_register(&lguest_bus.bus) != 0 + || device_register(&lguest_bus.dev) != 0) + panic("lguest bus registration failed"); + + scan_devices(); + return 0; +} +/* Do this after core stuff, before devices. */ +postcore_initcall(lguest_bus_init); diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c new file mode 100644 index 00000000000..80d1b58c769 --- /dev/null +++ b/drivers/lguest/lguest_user.c @@ -0,0 +1,382 @@ +/*P:200 This contains all the /dev/lguest code, whereby the userspace launcher + * controls and communicates with the Guest. For example, the first write will + * tell us the memory size, pagetable, entry point and kernel address offset. + * A read will run the Guest until a signal is pending (-EINTR), or the Guest + * does a DMA out to the Launcher. Writes are also used to get a DMA buffer + * registered by the Guest and to send the Guest an interrupt. :*/ +#include <linux/uaccess.h> +#include <linux/miscdevice.h> +#include <linux/fs.h> +#include "lg.h" + +/*L:030 setup_regs() doesn't really belong in this file, but it gives us an + * early glimpse deeper into the Host so it's worth having here. + * + * Most of the Guest's registers are left alone: we used get_zeroed_page() to + * allocate the structure, so they will be 0. */ +static void setup_regs(struct lguest_regs *regs, unsigned long start) +{ + /* There are four "segment" registers which the Guest needs to boot: + * The "code segment" register (cs) refers to the kernel code segment + * __KERNEL_CS, and the "data", "extra" and "stack" segment registers + * refer to the kernel data segment __KERNEL_DS. + * + * The privilege level is packed into the lower bits. The Guest runs + * at privilege level 1 (GUEST_PL).*/ + regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL; + regs->cs = __KERNEL_CS|GUEST_PL; + + /* The "eflags" register contains miscellaneous flags. Bit 1 (0x002) + * is supposed to always be "1". Bit 9 (0x200) controls whether + * interrupts are enabled. We always leave interrupts enabled while + * running the Guest. */ + regs->eflags = 0x202; + + /* The "Extended Instruction Pointer" register says where the Guest is + * running. */ + regs->eip = start; + + /* %esi points to our boot information, at physical address 0, so don't + * touch it. */ +} + +/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a + * DMA buffer. This is done by writing LHREQ_GETDMA and the key to + * /dev/lguest. */ +static long user_get_dma(struct lguest *lg, const u32 __user *input) +{ + unsigned long key, udma, irq; + + /* Fetch the key they wrote to us. */ + if (get_user(key, input) != 0) + return -EFAULT; + /* Look for a free Guest DMA buffer bound to that key. */ + udma = get_dma_buffer(lg, key, &irq); + if (!udma) + return -ENOENT; + + /* We need to tell the Launcher what interrupt the Guest expects after + * the buffer is filled. We stash it in udma->used_len. */ + lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq); + + /* The (guest-physical) address of the DMA buffer is returned from + * the write(). */ + return udma; +} + +/*L:315 To force the Guest to stop running and return to the Launcher, the + * Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest. The + * Launcher then writes LHREQ_BREAK and "0" to release the Waker. */ +static int break_guest_out(struct lguest *lg, const u32 __user *input) +{ + unsigned long on; + + /* Fetch whether they're turning break on or off.. */ + if (get_user(on, input) != 0) + return -EFAULT; + + if (on) { + lg->break_out = 1; + /* Pop it out (may be running on different CPU) */ + wake_up_process(lg->tsk); + /* Wait for them to reset it */ + return wait_event_interruptible(lg->break_wq, !lg->break_out); + } else { + lg->break_out = 0; + wake_up(&lg->break_wq); + return 0; + } +} + +/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt + * number to /dev/lguest. */ +static int user_send_irq(struct lguest *lg, const u32 __user *input) +{ + u32 irq; + + if (get_user(irq, input) != 0) + return -EFAULT; + if (irq >= LGUEST_IRQS) + return -EINVAL; + /* Next time the Guest runs, the core code will see if it can deliver + * this interrupt. */ + set_bit(irq, lg->irqs_pending); + return 0; +} + +/*L:040 Once our Guest is initialized, the Launcher makes it run by reading + * from /dev/lguest. */ +static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o) +{ + struct lguest *lg = file->private_data; + + /* You must write LHREQ_INITIALIZE first! */ + if (!lg) + return -EINVAL; + + /* If you're not the task which owns the guest, go away. */ + if (current != lg->tsk) + return -EPERM; + + /* If the guest is already dead, we indicate why */ + if (lg->dead) { + size_t len; + + /* lg->dead either contains an error code, or a string. */ + if (IS_ERR(lg->dead)) + return PTR_ERR(lg->dead); + + /* We can only return as much as the buffer they read with. */ + len = min(size, strlen(lg->dead)+1); + if (copy_to_user(user, lg->dead, len) != 0) + return -EFAULT; + return len; + } + + /* If we returned from read() last time because the Guest sent DMA, + * clear the flag. */ + if (lg->dma_is_pending) + lg->dma_is_pending = 0; + + /* Run the Guest until something interesting happens. */ + return run_guest(lg, (unsigned long __user *)user); +} + +/*L:020 The initialization write supplies 4 32-bit values (in addition to the + * 32-bit LHREQ_INITIALIZE value). These are: + * + * pfnlimit: The highest (Guest-physical) page number the Guest should be + * allowed to access. The Launcher has to live in Guest memory, so it sets + * this to ensure the Guest can't reach it. + * + * pgdir: The (Guest-physical) address of the top of the initial Guest + * pagetables (which are set up by the Launcher). + * + * start: The first instruction to execute ("eip" in x86-speak). + * + * page_offset: The PAGE_OFFSET constant in the Guest kernel. We should + * probably wean the code off this, but it's a very useful constant! Any + * address above this is within the Guest kernel, and any kernel address can + * quickly converted from physical to virtual by adding PAGE_OFFSET. It's + * 0xC0000000 (3G) by default, but it's configurable at kernel build time. + */ +static int initialize(struct file *file, const u32 __user *input) +{ + /* "struct lguest" contains everything we (the Host) know about a + * Guest. */ + struct lguest *lg; + int err, i; + u32 args[4]; + + /* We grab the Big Lguest lock, which protects the global array + * "lguests" and multiple simultaneous initializations. */ + mutex_lock(&lguest_lock); + /* You can't initialize twice! Close the device and start again... */ + if (file->private_data) { + err = -EBUSY; + goto unlock; + } + + if (copy_from_user(args, input, sizeof(args)) != 0) { + err = -EFAULT; + goto unlock; + } + + /* Find an unused guest. */ + i = find_free_guest(); + if (i < 0) { + err = -ENOSPC; + goto unlock; + } + /* OK, we have an index into the "lguest" array: "lg" is a convenient + * pointer. */ + lg = &lguests[i]; + + /* Populate the easy fields of our "struct lguest" */ + lg->guestid = i; + lg->pfn_limit = args[0]; + lg->page_offset = args[3]; + + /* We need a complete page for the Guest registers: they are accessible + * to the Guest and we can only grant it access to whole pages. */ + lg->regs_page = get_zeroed_page(GFP_KERNEL); + if (!lg->regs_page) { + err = -ENOMEM; + goto release_guest; + } + /* We actually put the registers at the bottom of the page. */ + lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs); + + /* Initialize the Guest's shadow page tables, using the toplevel + * address the Launcher gave us. This allocates memory, so can + * fail. */ + err = init_guest_pagetable(lg, args[1]); + if (err) + goto free_regs; + + /* Now we initialize the Guest's registers, handing it the start + * address. */ + setup_regs(lg->regs, args[2]); + + /* There are a couple of GDT entries the Guest expects when first + * booting. */ + setup_guest_gdt(lg); + + /* The timer for lguest's clock needs initialization. */ + init_clockdev(lg); + + /* We keep a pointer to the Launcher task (ie. current task) for when + * other Guests want to wake this one (inter-Guest I/O). */ + lg->tsk = current; + /* We need to keep a pointer to the Launcher's memory map, because if + * the Launcher dies we need to clean it up. If we don't keep a + * reference, it is destroyed before close() is called. */ + lg->mm = get_task_mm(lg->tsk); + + /* Initialize the queue for the waker to wait on */ + init_waitqueue_head(&lg->break_wq); + + /* We remember which CPU's pages this Guest used last, for optimization + * when the same Guest runs on the same CPU twice. */ + lg->last_pages = NULL; + + /* We keep our "struct lguest" in the file's private_data. */ + file->private_data = lg; + + mutex_unlock(&lguest_lock); + + /* And because this is a write() call, we return the length used. */ + return sizeof(args); + +free_regs: + free_page(lg->regs_page); +release_guest: + memset(lg, 0, sizeof(*lg)); +unlock: + mutex_unlock(&lguest_lock); + return err; +} + +/*L:010 The first operation the Launcher does must be a write. All writes + * start with a 32 bit number: for the first write this must be + * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use + * writes of other values to get DMA buffers and send interrupts. */ +static ssize_t write(struct file *file, const char __user *input, + size_t size, loff_t *off) +{ + /* Once the guest is initialized, we hold the "struct lguest" in the + * file private data. */ + struct lguest *lg = file->private_data; + u32 req; + + if (get_user(req, input) != 0) + return -EFAULT; + input += sizeof(req); + + /* If you haven't initialized, you must do that first. */ + if (req != LHREQ_INITIALIZE && !lg) + return -EINVAL; + + /* Once the Guest is dead, all you can do is read() why it died. */ + if (lg && lg->dead) + return -ENOENT; + + /* If you're not the task which owns the Guest, you can only break */ + if (lg && current != lg->tsk && req != LHREQ_BREAK) + return -EPERM; + + switch (req) { + case LHREQ_INITIALIZE: + return initialize(file, (const u32 __user *)input); + case LHREQ_GETDMA: + return user_get_dma(lg, (const u32 __user *)input); + case LHREQ_IRQ: + return user_send_irq(lg, (const u32 __user *)input); + case LHREQ_BREAK: + return break_guest_out(lg, (const u32 __user *)input); + default: + return -EINVAL; + } +} + +/*L:060 The final piece of interface code is the close() routine. It reverses + * everything done in initialize(). This is usually called because the + * Launcher exited. + * + * Note that the close routine returns 0 or a negative error number: it can't + * really fail, but it can whine. I blame Sun for this wart, and K&R C for + * letting them do it. :*/ +static int close(struct inode *inode, struct file *file) +{ + struct lguest *lg = file->private_data; + + /* If we never successfully initialized, there's nothing to clean up */ + if (!lg) + return 0; + + /* We need the big lock, to protect from inter-guest I/O and other + * Launchers initializing guests. */ + mutex_lock(&lguest_lock); + /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */ + hrtimer_cancel(&lg->hrt); + /* Free any DMA buffers the Guest had bound. */ + release_all_dma(lg); + /* Free up the shadow page tables for the Guest. */ + free_guest_pagetable(lg); + /* Now all the memory cleanups are done, it's safe to release the + * Launcher's memory management structure. */ + mmput(lg->mm); + /* If lg->dead doesn't contain an error code it will be NULL or a + * kmalloc()ed string, either of which is ok to hand to kfree(). */ + if (!IS_ERR(lg->dead)) + kfree(lg->dead); + /* We can free up the register page we allocated. */ + free_page(lg->regs_page); + /* We clear the entire structure, which also marks it as free for the + * next user. */ + memset(lg, 0, sizeof(*lg)); + /* Release lock and exit. */ + mutex_unlock(&lguest_lock); + + return 0; +} + +/*L:000 + * Welcome to our journey through the Launcher! + * + * The Launcher is the Host userspace program which sets up, runs and services + * the Guest. In fact, many comments in the Drivers which refer to "the Host" + * doing things are inaccurate: the Launcher does all the device handling for + * the Guest. The Guest can't tell what's done by the the Launcher and what by + * the Host. + * + * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we + * shall see more of that later. + * + * We begin our understanding with the Host kernel interface which the Launcher + * uses: reading and writing a character device called /dev/lguest. All the + * work happens in the read(), write() and close() routines: */ +static struct file_operations lguest_fops = { + .owner = THIS_MODULE, + .release = close, + .write = write, + .read = read, +}; + +/* This is a textbook example of a "misc" character device. Populate a "struct + * miscdevice" and register it with misc_register(). */ +static struct miscdevice lguest_dev = { + .minor = MISC_DYNAMIC_MINOR, + .name = "lguest", + .fops = &lguest_fops, +}; + +int __init lguest_device_init(void) +{ + return misc_register(&lguest_dev); +} + +void __exit lguest_device_remove(void) +{ + misc_deregister(&lguest_dev); +} diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c new file mode 100644 index 00000000000..b7a924ace68 --- /dev/null +++ b/drivers/lguest/page_tables.c @@ -0,0 +1,680 @@ +/*P:700 The pagetable code, on the other hand, still shows the scars of + * previous encounters. It's functional, and as neat as it can be in the + * circumstances, but be wary, for these things are subtle and break easily. + * The Guest provides a virtual to physical mapping, but we can neither trust + * it nor use it: we verify and convert it here to point the hardware to the + * actual Guest pages when running the Guest. :*/ + +/* Copyright (C) Rusty Russell IBM Corporation 2006. + * GPL v2 and any later version */ +#include <linux/mm.h> +#include <linux/types.h> +#include <linux/spinlock.h> +#include <linux/random.h> +#include <linux/percpu.h> +#include <asm/tlbflush.h> +#include "lg.h" + +/*M:008 We hold reference to pages, which prevents them from being swapped. + * It'd be nice to have a callback in the "struct mm_struct" when Linux wants + * to swap out. If we had this, and a shrinker callback to trim PTE pages, we + * could probably consider launching Guests as non-root. :*/ + +/*H:300 + * The Page Table Code + * + * We use two-level page tables for the Guest. If you're not entirely + * comfortable with virtual addresses, physical addresses and page tables then + * I recommend you review lguest.c's "Page Table Handling" (with diagrams!). + * + * The Guest keeps page tables, but we maintain the actual ones here: these are + * called "shadow" page tables. Which is a very Guest-centric name: these are + * the real page tables the CPU uses, although we keep them up to date to + * reflect the Guest's. (See what I mean about weird naming? Since when do + * shadows reflect anything?) + * + * Anyway, this is the most complicated part of the Host code. There are seven + * parts to this: + * (i) Setting up a page table entry for the Guest when it faults, + * (ii) Setting up the page table entry for the Guest stack, + * (iii) Setting up a page table entry when the Guest tells us it has changed, + * (iv) Switching page tables, + * (v) Flushing (thowing away) page tables, + * (vi) Mapping the Switcher when the Guest is about to run, + * (vii) Setting up the page tables initially. + :*/ + +/* Pages a 4k long, and each page table entry is 4 bytes long, giving us 1024 + * (or 2^10) entries per page. */ +#define PTES_PER_PAGE_SHIFT 10 +#define PTES_PER_PAGE (1 << PTES_PER_PAGE_SHIFT) + +/* 1024 entries in a page table page maps 1024 pages: 4MB. The Switcher is + * conveniently placed at the top 4MB, so it uses a separate, complete PTE + * page. */ +#define SWITCHER_PGD_INDEX (PTES_PER_PAGE - 1) + +/* We actually need a separate PTE page for each CPU. Remember that after the + * Switcher code itself comes two pages for each CPU, and we don't want this + * CPU's guest to see the pages of any other CPU. */ +static DEFINE_PER_CPU(spte_t *, switcher_pte_pages); +#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu) + +/*H:320 With our shadow and Guest types established, we need to deal with + * them: the page table code is curly enough to need helper functions to keep + * it clear and clean. + * + * The first helper takes a virtual address, and says which entry in the top + * level page table deals with that address. Since each top level entry deals + * with 4M, this effectively divides by 4M. */ +static unsigned vaddr_to_pgd_index(unsigned long vaddr) +{ + return vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT); +} + +/* There are two functions which return pointers to the shadow (aka "real") + * page tables. + * + * spgd_addr() takes the virtual address and returns a pointer to the top-level + * page directory entry for that address. Since we keep track of several page + * tables, the "i" argument tells us which one we're interested in (it's + * usually the current one). */ +static spgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr) +{ + unsigned int index = vaddr_to_pgd_index(vaddr); + + /* We kill any Guest trying to touch the Switcher addresses. */ + if (index >= SWITCHER_PGD_INDEX) { + kill_guest(lg, "attempt to access switcher pages"); + index = 0; + } + /* Return a pointer index'th pgd entry for the i'th page table. */ + return &lg->pgdirs[i].pgdir[index]; +} + +/* This routine then takes the PGD entry given above, which contains the + * address of the PTE page. It then returns a pointer to the PTE entry for the + * given address. */ +static spte_t *spte_addr(struct lguest *lg, spgd_t spgd, unsigned long vaddr) +{ + spte_t *page = __va(spgd.pfn << PAGE_SHIFT); + /* You should never call this if the PGD entry wasn't valid */ + BUG_ON(!(spgd.flags & _PAGE_PRESENT)); + return &page[(vaddr >> PAGE_SHIFT) % PTES_PER_PAGE]; +} + +/* These two functions just like the above two, except they access the Guest + * page tables. Hence they return a Guest address. */ +static unsigned long gpgd_addr(struct lguest *lg, unsigned long vaddr) +{ + unsigned int index = vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT); + return lg->pgdirs[lg->pgdidx].cr3 + index * sizeof(gpgd_t); +} + +static unsigned long gpte_addr(struct lguest *lg, + gpgd_t gpgd, unsigned long vaddr) +{ + unsigned long gpage = gpgd.pfn << PAGE_SHIFT; + BUG_ON(!(gpgd.flags & _PAGE_PRESENT)); + return gpage + ((vaddr>>PAGE_SHIFT) % PTES_PER_PAGE) * sizeof(gpte_t); +} + +/*H:350 This routine takes a page number given by the Guest and converts it to + * an actual, physical page number. It can fail for several reasons: the + * virtual address might not be mapped by the Launcher, the write flag is set + * and the page is read-only, or the write flag was set and the page was + * shared so had to be copied, but we ran out of memory. + * + * This holds a reference to the page, so release_pte() is careful to + * put that back. */ +static unsigned long get_pfn(unsigned long virtpfn, int write) +{ + struct page *page; + /* This value indicates failure. */ + unsigned long ret = -1UL; + + /* get_user_pages() is a complex interface: it gets the "struct + * vm_area_struct" and "struct page" assocated with a range of pages. + * It also needs the task's mmap_sem held, and is not very quick. + * It returns the number of pages it got. */ + down_read(¤t->mm->mmap_sem); + if (get_user_pages(current, current->mm, virtpfn << PAGE_SHIFT, + 1, write, 1, &page, NULL) == 1) + ret = page_to_pfn(page); + up_read(¤t->mm->mmap_sem); + return ret; +} + +/*H:340 Converting a Guest page table entry to a shadow (ie. real) page table + * entry can be a little tricky. The flags are (almost) the same, but the + * Guest PTE contains a virtual page number: the CPU needs the real page + * number. */ +static spte_t gpte_to_spte(struct lguest *lg, gpte_t gpte, int write) +{ + spte_t spte; + unsigned long pfn; + + /* The Guest sets the global flag, because it thinks that it is using + * PGE. We only told it to use PGE so it would tell us whether it was + * flushing a kernel mapping or a userspace mapping. We don't actually + * use the global bit, so throw it away. */ + spte.flags = (gpte.flags & ~_PAGE_GLOBAL); + + /* We need a temporary "unsigned long" variable to hold the answer from + * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't + * fit in spte.pfn. get_pfn() finds the real physical number of the + * page, given the virtual number. */ + pfn = get_pfn(gpte.pfn, write); + if (pfn == -1UL) { + kill_guest(lg, "failed to get page %u", gpte.pfn); + /* When we destroy the Guest, we'll go through the shadow page + * tables and release_pte() them. Make sure we don't think + * this one is valid! */ + spte.flags = 0; + } + /* Now we assign the page number, and our shadow PTE is complete. */ + spte.pfn = pfn; + return spte; +} + +/*H:460 And to complete the chain, release_pte() looks like this: */ +static void release_pte(spte_t pte) +{ + /* Remember that get_user_pages() took a reference to the page, in + * get_pfn()? We have to put it back now. */ + if (pte.flags & _PAGE_PRESENT) + put_page(pfn_to_page(pte.pfn)); +} +/*:*/ + +static void check_gpte(struct lguest *lg, gpte_t gpte) +{ + if ((gpte.flags & (_PAGE_PWT|_PAGE_PSE)) || gpte.pfn >= lg->pfn_limit) + kill_guest(lg, "bad page table entry"); +} + +static void check_gpgd(struct lguest *lg, gpgd_t gpgd) +{ + if ((gpgd.flags & ~_PAGE_TABLE) || gpgd.pfn >= lg->pfn_limit) + kill_guest(lg, "bad page directory entry"); +} + +/*H:330 + * (i) Setting up a page table entry for the Guest when it faults + * + * We saw this call in run_guest(): when we see a page fault in the Guest, we + * come here. That's because we only set up the shadow page tables lazily as + * they're needed, so we get page faults all the time and quietly fix them up + * and return to the Guest without it knowing. + * + * If we fixed up the fault (ie. we mapped the address), this routine returns + * true. */ +int demand_page(struct lguest *lg, unsigned long vaddr, int errcode) +{ + gpgd_t gpgd; + spgd_t *spgd; + unsigned long gpte_ptr; + gpte_t gpte; + spte_t *spte; + + /* First step: get the top-level Guest page table entry. */ + gpgd = mkgpgd(lgread_u32(lg, gpgd_addr(lg, vaddr))); + /* Toplevel not present? We can't map it in. */ + if (!(gpgd.flags & _PAGE_PRESENT)) + return 0; + + /* Now look at the matching shadow entry. */ + spgd = spgd_addr(lg, lg->pgdidx, vaddr); + if (!(spgd->flags & _PAGE_PRESENT)) { + /* No shadow entry: allocate a new shadow PTE page. */ + unsigned long ptepage = get_zeroed_page(GFP_KERNEL); + /* This is not really the Guest's fault, but killing it is + * simple for this corner case. */ + if (!ptepage) { + kill_guest(lg, "out of memory allocating pte page"); + return 0; + } + /* We check that the Guest pgd is OK. */ + check_gpgd(lg, gpgd); + /* And we copy the flags to the shadow PGD entry. The page + * number in the shadow PGD is the page we just allocated. */ + spgd->raw.val = (__pa(ptepage) | gpgd.flags); + } + + /* OK, now we look at the lower level in the Guest page table: keep its + * address, because we might update it later. */ + gpte_ptr = gpte_addr(lg, gpgd, vaddr); + gpte = mkgpte(lgread_u32(lg, gpte_ptr)); + + /* If this page isn't in the Guest page tables, we can't page it in. */ + if (!(gpte.flags & _PAGE_PRESENT)) + return 0; + + /* Check they're not trying to write to a page the Guest wants + * read-only (bit 2 of errcode == write). */ + if ((errcode & 2) && !(gpte.flags & _PAGE_RW)) + return 0; + + /* User access to a kernel page? (bit 3 == user access) */ + if ((errcode & 4) && !(gpte.flags & _PAGE_USER)) + return 0; + + /* Check that the Guest PTE flags are OK, and the page number is below + * the pfn_limit (ie. not mapping the Launcher binary). */ + check_gpte(lg, gpte); + /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */ + gpte.flags |= _PAGE_ACCESSED; + if (errcode & 2) + gpte.flags |= _PAGE_DIRTY; + + /* Get the pointer to the shadow PTE entry we're going to set. */ + spte = spte_addr(lg, *spgd, vaddr); + /* If there was a valid shadow PTE entry here before, we release it. + * This can happen with a write to a previously read-only entry. */ + release_pte(*spte); + + /* If this is a write, we insist that the Guest page is writable (the + * final arg to gpte_to_spte()). */ + if (gpte.flags & _PAGE_DIRTY) + *spte = gpte_to_spte(lg, gpte, 1); + else { + /* If this is a read, don't set the "writable" bit in the page + * table entry, even if the Guest says it's writable. That way + * we come back here when a write does actually ocur, so we can + * update the Guest's _PAGE_DIRTY flag. */ + gpte_t ro_gpte = gpte; + ro_gpte.flags &= ~_PAGE_RW; + *spte = gpte_to_spte(lg, ro_gpte, 0); + } + + /* Finally, we write the Guest PTE entry back: we've set the + * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */ + lgwrite_u32(lg, gpte_ptr, gpte.raw.val); + + /* We succeeded in mapping the page! */ + return 1; +} + +/*H:360 (ii) Setting up the page table entry for the Guest stack. + * + * Remember pin_stack_pages() which makes sure the stack is mapped? It could + * simply call demand_page(), but as we've seen that logic is quite long, and + * usually the stack pages are already mapped anyway, so it's not required. + * + * This is a quick version which answers the question: is this virtual address + * mapped by the shadow page tables, and is it writable? */ +static int page_writable(struct lguest *lg, unsigned long vaddr) +{ + spgd_t *spgd; + unsigned long flags; + + /* Look at the top level entry: is it present? */ + spgd = spgd_addr(lg, lg->pgdidx, vaddr); + if (!(spgd->flags & _PAGE_PRESENT)) + return 0; + + /* Check the flags on the pte entry itself: it must be present and + * writable. */ + flags = spte_addr(lg, *spgd, vaddr)->flags; + return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW); +} + +/* So, when pin_stack_pages() asks us to pin a page, we check if it's already + * in the page tables, and if not, we call demand_page() with error code 2 + * (meaning "write"). */ +void pin_page(struct lguest *lg, unsigned long vaddr) +{ + if (!page_writable(lg, vaddr) && !demand_page(lg, vaddr, 2)) + kill_guest(lg, "bad stack page %#lx", vaddr); +} + +/*H:450 If we chase down the release_pgd() code, it looks like this: */ +static void release_pgd(struct lguest *lg, spgd_t *spgd) +{ + /* If the entry's not present, there's nothing to release. */ + if (spgd->flags & _PAGE_PRESENT) { + unsigned int i; + /* Converting the pfn to find the actual PTE page is easy: turn + * the page number into a physical address, then convert to a + * virtual address (easy for kernel pages like this one). */ + spte_t *ptepage = __va(spgd->pfn << PAGE_SHIFT); + /* For each entry in the page, we might need to release it. */ + for (i = 0; i < PTES_PER_PAGE; i++) + release_pte(ptepage[i]); + /* Now we can free the page of PTEs */ + free_page((long)ptepage); + /* And zero out the PGD entry we we never release it twice. */ + spgd->raw.val = 0; + } +} + +/*H:440 (v) Flushing (thowing away) page tables, + * + * We saw flush_user_mappings() called when we re-used a top-level pgdir page. + * It simply releases every PTE page from 0 up to the kernel address. */ +static void flush_user_mappings(struct lguest *lg, int idx) +{ + unsigned int i; + /* Release every pgd entry up to the kernel's address. */ + for (i = 0; i < vaddr_to_pgd_index(lg->page_offset); i++) + release_pgd(lg, lg->pgdirs[idx].pgdir + i); +} + +/* The Guest also has a hypercall to do this manually: it's used when a large + * number of mappings have been changed. */ +void guest_pagetable_flush_user(struct lguest *lg) +{ + /* Drop the userspace part of the current page table. */ + flush_user_mappings(lg, lg->pgdidx); +} +/*:*/ + +/* We keep several page tables. This is a simple routine to find the page + * table (if any) corresponding to this top-level address the Guest has given + * us. */ +static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable) +{ + unsigned int i; + for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) + if (lg->pgdirs[i].cr3 == pgtable) + break; + return i; +} + +/*H:435 And this is us, creating the new page directory. If we really do + * allocate a new one (and so the kernel parts are not there), we set + * blank_pgdir. */ +static unsigned int new_pgdir(struct lguest *lg, + unsigned long cr3, + int *blank_pgdir) +{ + unsigned int next; + + /* We pick one entry at random to throw out. Choosing the Least + * Recently Used might be better, but this is easy. */ + next = random32() % ARRAY_SIZE(lg->pgdirs); + /* If it's never been allocated at all before, try now. */ + if (!lg->pgdirs[next].pgdir) { + lg->pgdirs[next].pgdir = (spgd_t *)get_zeroed_page(GFP_KERNEL); + /* If the allocation fails, just keep using the one we have */ + if (!lg->pgdirs[next].pgdir) + next = lg->pgdidx; + else + /* This is a blank page, so there are no kernel + * mappings: caller must map the stack! */ + *blank_pgdir = 1; + } + /* Record which Guest toplevel this shadows. */ + lg->pgdirs[next].cr3 = cr3; + /* Release all the non-kernel mappings. */ + flush_user_mappings(lg, next); + + return next; +} + +/*H:430 (iv) Switching page tables + * + * This is what happens when the Guest changes page tables (ie. changes the + * top-level pgdir). This happens on almost every context switch. */ +void guest_new_pagetable(struct lguest *lg, unsigned long pgtable) +{ + int newpgdir, repin = 0; + + /* Look to see if we have this one already. */ + newpgdir = find_pgdir(lg, pgtable); + /* If not, we allocate or mug an existing one: if it's a fresh one, + * repin gets set to 1. */ + if (newpgdir == ARRAY_SIZE(lg->pgdirs)) + newpgdir = new_pgdir(lg, pgtable, &repin); + /* Change the current pgd index to the new one. */ + lg->pgdidx = newpgdir; + /* If it was completely blank, we map in the Guest kernel stack */ + if (repin) + pin_stack_pages(lg); +} + +/*H:470 Finally, a routine which throws away everything: all PGD entries in all + * the shadow page tables. This is used when we destroy the Guest. */ +static void release_all_pagetables(struct lguest *lg) +{ + unsigned int i, j; + + /* Every shadow pagetable this Guest has */ + for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) + if (lg->pgdirs[i].pgdir) + /* Every PGD entry except the Switcher at the top */ + for (j = 0; j < SWITCHER_PGD_INDEX; j++) + release_pgd(lg, lg->pgdirs[i].pgdir + j); +} + +/* We also throw away everything when a Guest tells us it's changed a kernel + * mapping. Since kernel mappings are in every page table, it's easiest to + * throw them all away. This is amazingly slow, but thankfully rare. */ +void guest_pagetable_clear_all(struct lguest *lg) +{ + release_all_pagetables(lg); + /* We need the Guest kernel stack mapped again. */ + pin_stack_pages(lg); +} + +/*H:420 This is the routine which actually sets the page table entry for then + * "idx"'th shadow page table. + * + * Normally, we can just throw out the old entry and replace it with 0: if they + * use it demand_page() will put the new entry in. We need to do this anyway: + * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page + * is read from, and _PAGE_DIRTY when it's written to. + * + * But Avi Kivity pointed out that most Operating Systems (Linux included) set + * these bits on PTEs immediately anyway. This is done to save the CPU from + * having to update them, but it helps us the same way: if they set + * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if + * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately. + */ +static void do_set_pte(struct lguest *lg, int idx, + unsigned long vaddr, gpte_t gpte) +{ + /* Look up the matching shadow page directot entry. */ + spgd_t *spgd = spgd_addr(lg, idx, vaddr); + + /* If the top level isn't present, there's no entry to update. */ + if (spgd->flags & _PAGE_PRESENT) { + /* Otherwise, we start by releasing the existing entry. */ + spte_t *spte = spte_addr(lg, *spgd, vaddr); + release_pte(*spte); + + /* If they're setting this entry as dirty or accessed, we might + * as well put that entry they've given us in now. This shaves + * 10% off a copy-on-write micro-benchmark. */ + if (gpte.flags & (_PAGE_DIRTY | _PAGE_ACCESSED)) { + check_gpte(lg, gpte); + *spte = gpte_to_spte(lg, gpte, gpte.flags&_PAGE_DIRTY); + } else + /* Otherwise we can demand_page() it in later. */ + spte->raw.val = 0; + } +} + +/*H:410 Updating a PTE entry is a little trickier. + * + * We keep track of several different page tables (the Guest uses one for each + * process, so it makes sense to cache at least a few). Each of these have + * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for + * all processes. So when the page table above that address changes, we update + * all the page tables, not just the current one. This is rare. + * + * The benefit is that when we have to track a new page table, we can copy keep + * all the kernel mappings. This speeds up context switch immensely. */ +void guest_set_pte(struct lguest *lg, + unsigned long cr3, unsigned long vaddr, gpte_t gpte) +{ + /* Kernel mappings must be changed on all top levels. Slow, but + * doesn't happen often. */ + if (vaddr >= lg->page_offset) { + unsigned int i; + for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) + if (lg->pgdirs[i].pgdir) + do_set_pte(lg, i, vaddr, gpte); + } else { + /* Is this page table one we have a shadow for? */ + int pgdir = find_pgdir(lg, cr3); + if (pgdir != ARRAY_SIZE(lg->pgdirs)) + /* If so, do the update. */ + do_set_pte(lg, pgdir, vaddr, gpte); + } +} + +/*H:400 + * (iii) Setting up a page table entry when the Guest tells us it has changed. + * + * Just like we did in interrupts_and_traps.c, it makes sense for us to deal + * with the other side of page tables while we're here: what happens when the + * Guest asks for a page table to be updated? + * + * We already saw that demand_page() will fill in the shadow page tables when + * needed, so we can simply remove shadow page table entries whenever the Guest + * tells us they've changed. When the Guest tries to use the new entry it will + * fault and demand_page() will fix it up. + * + * So with that in mind here's our code to to update a (top-level) PGD entry: + */ +void guest_set_pmd(struct lguest *lg, unsigned long cr3, u32 idx) +{ + int pgdir; + + /* The kernel seems to try to initialize this early on: we ignore its + * attempts to map over the Switcher. */ + if (idx >= SWITCHER_PGD_INDEX) + return; + + /* If they're talking about a page table we have a shadow for... */ + pgdir = find_pgdir(lg, cr3); + if (pgdir < ARRAY_SIZE(lg->pgdirs)) + /* ... throw it away. */ + release_pgd(lg, lg->pgdirs[pgdir].pgdir + idx); +} + +/*H:500 (vii) Setting up the page tables initially. + * + * When a Guest is first created, the Launcher tells us where the toplevel of + * its first page table is. We set some things up here: */ +int init_guest_pagetable(struct lguest *lg, unsigned long pgtable) +{ + /* In flush_user_mappings() we loop from 0 to + * "vaddr_to_pgd_index(lg->page_offset)". This assumes it won't hit + * the Switcher mappings, so check that now. */ + if (vaddr_to_pgd_index(lg->page_offset) >= SWITCHER_PGD_INDEX) + return -EINVAL; + /* We start on the first shadow page table, and give it a blank PGD + * page. */ + lg->pgdidx = 0; + lg->pgdirs[lg->pgdidx].cr3 = pgtable; + lg->pgdirs[lg->pgdidx].pgdir = (spgd_t*)get_zeroed_page(GFP_KERNEL); + if (!lg->pgdirs[lg->pgdidx].pgdir) + return -ENOMEM; + return 0; +} + +/* When a Guest dies, our cleanup is fairly simple. */ +void free_guest_pagetable(struct lguest *lg) +{ + unsigned int i; + + /* Throw away all page table pages. */ + release_all_pagetables(lg); + /* Now free the top levels: free_page() can handle 0 just fine. */ + for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) + free_page((long)lg->pgdirs[i].pgdir); +} + +/*H:480 (vi) Mapping the Switcher when the Guest is about to run. + * + * The Switcher and the two pages for this CPU need to be available to the + * Guest (and not the pages for other CPUs). We have the appropriate PTE pages + * for each CPU already set up, we just need to hook them in. */ +void map_switcher_in_guest(struct lguest *lg, struct lguest_pages *pages) +{ + spte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages); + spgd_t switcher_pgd; + spte_t regs_pte; + + /* Make the last PGD entry for this Guest point to the Switcher's PTE + * page for this CPU (with appropriate flags). */ + switcher_pgd.pfn = __pa(switcher_pte_page) >> PAGE_SHIFT; + switcher_pgd.flags = _PAGE_KERNEL; + lg->pgdirs[lg->pgdidx].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd; + + /* We also change the Switcher PTE page. When we're running the Guest, + * we want the Guest's "regs" page to appear where the first Switcher + * page for this CPU is. This is an optimization: when the Switcher + * saves the Guest registers, it saves them into the first page of this + * CPU's "struct lguest_pages": if we make sure the Guest's register + * page is already mapped there, we don't have to copy them out + * again. */ + regs_pte.pfn = __pa(lg->regs_page) >> PAGE_SHIFT; + regs_pte.flags = _PAGE_KERNEL; + switcher_pte_page[(unsigned long)pages/PAGE_SIZE%PTES_PER_PAGE] + = regs_pte; +} +/*:*/ + +static void free_switcher_pte_pages(void) +{ + unsigned int i; + + for_each_possible_cpu(i) + free_page((long)switcher_pte_page(i)); +} + +/*H:520 Setting up the Switcher PTE page for given CPU is fairly easy, given + * the CPU number and the "struct page"s for the Switcher code itself. + * + * Currently the Switcher is less than a page long, so "pages" is always 1. */ +static __init void populate_switcher_pte_page(unsigned int cpu, + struct page *switcher_page[], + unsigned int pages) +{ + unsigned int i; + spte_t *pte = switcher_pte_page(cpu); + + /* The first entries are easy: they map the Switcher code. */ + for (i = 0; i < pages; i++) { + pte[i].pfn = page_to_pfn(switcher_page[i]); + pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED; + } + + /* The only other thing we map is this CPU's pair of pages. */ + i = pages + cpu*2; + + /* First page (Guest registers) is writable from the Guest */ + pte[i].pfn = page_to_pfn(switcher_page[i]); + pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW; + /* The second page contains the "struct lguest_ro_state", and is + * read-only. */ + pte[i+1].pfn = page_to_pfn(switcher_page[i+1]); + pte[i+1].flags = _PAGE_PRESENT|_PAGE_ACCESSED; +} + +/*H:510 At boot or module load time, init_pagetables() allocates and populates + * the Switcher PTE page for each CPU. */ +__init int init_pagetables(struct page **switcher_page, unsigned int pages) +{ + unsigned int i; + + for_each_possible_cpu(i) { + switcher_pte_page(i) = (spte_t *)get_zeroed_page(GFP_KERNEL); + if (!switcher_pte_page(i)) { + free_switcher_pte_pages(); + return -ENOMEM; + } + populate_switcher_pte_page(i, switcher_page, pages); + } + return 0; +} +/*:*/ + +/* Cleaning up simply involves freeing the PTE page for each CPU. */ +void free_pagetables(void) +{ + free_switcher_pte_pages(); +} diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c new file mode 100644 index 00000000000..9b81119f46e --- /dev/null +++ b/drivers/lguest/segments.c @@ -0,0 +1,177 @@ +/*P:600 The x86 architecture has segments, which involve a table of descriptors + * which can be used to do funky things with virtual address interpretation. + * We originally used to use segments so the Guest couldn't alter the + * Guest<->Host Switcher, and then we had to trim Guest segments, and restore + * for userspace per-thread segments, but trim again for on userspace->kernel + * transitions... This nightmarish creation was contained within this file, + * where we knew not to tread without heavy armament and a change of underwear. + * + * In these modern times, the segment handling code consists of simple sanity + * checks, and the worst you'll experience reading this code is butterfly-rash + * from frolicking through its parklike serenity. :*/ +#include "lg.h" + +/*H:600 + * We've almost completed the Host; there's just one file to go! + * + * Segments & The Global Descriptor Table + * + * (That title sounds like a bad Nerdcore group. Not to suggest that there are + * any good Nerdcore groups, but in high school a friend of mine had a band + * called Joe Fish and the Chips, so there are definitely worse band names). + * + * To refresh: the GDT is a table of 8-byte values describing segments. Once + * set up, these segments can be loaded into one of the 6 "segment registers". + * + * GDT entries are passed around as "struct desc_struct"s, which like IDT + * entries are split into two 32-bit members, "a" and "b". One day, someone + * will clean that up, and be declared a Hero. (No pressure, I'm just saying). + * + * Anyway, the GDT entry contains a base (the start address of the segment), a + * limit (the size of the segment - 1), and some flags. Sounds simple, and it + * would be, except those zany Intel engineers decided that it was too boring + * to put the base at one end, the limit at the other, and the flags in + * between. They decided to shotgun the bits at random throughout the 8 bytes, + * like so: + * + * 0 16 40 48 52 56 63 + * [ limit part 1 ][ base part 1 ][ flags ][li][fl][base ] + * mit ags part 2 + * part 2 + * + * As a result, this file contains a certain amount of magic numeracy. Let's + * begin. + */ + +/* There are several entries we don't let the Guest set. The TSS entry is the + * "Task State Segment" which controls all kinds of delicate things. The + * LGUEST_CS and LGUEST_DS entries are reserved for the Switcher, and the + * the Guest can't be trusted to deal with double faults. */ +static int ignored_gdt(unsigned int num) +{ + return (num == GDT_ENTRY_TSS + || num == GDT_ENTRY_LGUEST_CS + || num == GDT_ENTRY_LGUEST_DS + || num == GDT_ENTRY_DOUBLEFAULT_TSS); +} + +/*H:610 Once the GDT has been changed, we fix the new entries up a little. We + * don't care if they're invalid: the worst that can happen is a General + * Protection Fault in the Switcher when it restores a Guest segment register + * which tries to use that entry. Then we kill the Guest for causing such a + * mess: the message will be "unhandled trap 256". */ +static void fixup_gdt_table(struct lguest *lg, unsigned start, unsigned end) +{ + unsigned int i; + + for (i = start; i < end; i++) { + /* We never copy these ones to real GDT, so we don't care what + * they say */ + if (ignored_gdt(i)) + continue; + + /* Segment descriptors contain a privilege level: the Guest is + * sometimes careless and leaves this as 0, even though it's + * running at privilege level 1. If so, we fix it here. */ + if ((lg->gdt[i].b & 0x00006000) == 0) + lg->gdt[i].b |= (GUEST_PL << 13); + + /* Each descriptor has an "accessed" bit. If we don't set it + * now, the CPU will try to set it when the Guest first loads + * that entry into a segment register. But the GDT isn't + * writable by the Guest, so bad things can happen. */ + lg->gdt[i].b |= 0x00000100; + } +} + +/* This routine is called at boot or modprobe time for each CPU to set up the + * "constant" GDT entries for Guests running on that CPU. */ +void setup_default_gdt_entries(struct lguest_ro_state *state) +{ + struct desc_struct *gdt = state->guest_gdt; + unsigned long tss = (unsigned long)&state->guest_tss; + + /* The hypervisor segments are full 0-4G segments, privilege level 0 */ + gdt[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT; + gdt[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT; + + /* The TSS segment refers to the TSS entry for this CPU, so we cannot + * copy it from the Guest. Forgive the magic flags */ + gdt[GDT_ENTRY_TSS].a = 0x00000067 | (tss << 16); + gdt[GDT_ENTRY_TSS].b = 0x00008900 | (tss & 0xFF000000) + | ((tss >> 16) & 0x000000FF); +} + +/* This routine is called before the Guest is run for the first time. */ +void setup_guest_gdt(struct lguest *lg) +{ + /* Start with full 0-4G segments... */ + lg->gdt[GDT_ENTRY_KERNEL_CS] = FULL_EXEC_SEGMENT; + lg->gdt[GDT_ENTRY_KERNEL_DS] = FULL_SEGMENT; + /* ...except the Guest is allowed to use them, so set the privilege + * level appropriately in the flags. */ + lg->gdt[GDT_ENTRY_KERNEL_CS].b |= (GUEST_PL << 13); + lg->gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13); +} + +/* Like the IDT, we never simply use the GDT the Guest gives us. We set up the + * GDTs for each CPU, then we copy across the entries each time we want to run + * a different Guest on that CPU. */ + +/* A partial GDT load, for the three "thead-local storage" entries. Otherwise + * it's just like load_guest_gdt(). So much, in fact, it would probably be + * neater to have a single hypercall to cover both. */ +void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt) +{ + unsigned int i; + + for (i = GDT_ENTRY_TLS_MIN; i <= GDT_ENTRY_TLS_MAX; i++) + gdt[i] = lg->gdt[i]; +} + +/* This is the full version */ +void copy_gdt(const struct lguest *lg, struct desc_struct *gdt) +{ + unsigned int i; + + /* The default entries from setup_default_gdt_entries() are not + * replaced. See ignored_gdt() above. */ + for (i = 0; i < GDT_ENTRIES; i++) + if (!ignored_gdt(i)) + gdt[i] = lg->gdt[i]; +} + +/* This is where the Guest asks us to load a new GDT (LHCALL_LOAD_GDT). */ +void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num) +{ + /* We assume the Guest has the same number of GDT entries as the + * Host, otherwise we'd have to dynamically allocate the Guest GDT. */ + if (num > ARRAY_SIZE(lg->gdt)) + kill_guest(lg, "too many gdt entries %i", num); + + /* We read the whole thing in, then fix it up. */ + lgread(lg, lg->gdt, table, num * sizeof(lg->gdt[0])); + fixup_gdt_table(lg, 0, ARRAY_SIZE(lg->gdt)); + /* Mark that the GDT changed so the core knows it has to copy it again, + * even if the Guest is run on the same CPU. */ + lg->changed |= CHANGED_GDT; +} + +void guest_load_tls(struct lguest *lg, unsigned long gtls) +{ + struct desc_struct *tls = &lg->gdt[GDT_ENTRY_TLS_MIN]; + + lgread(lg, tls, gtls, sizeof(*tls)*GDT_ENTRY_TLS_ENTRIES); + fixup_gdt_table(lg, GDT_ENTRY_TLS_MIN, GDT_ENTRY_TLS_MAX+1); + lg->changed |= CHANGED_GDT_TLS; +} + +/* + * With this, we have finished the Host. + * + * Five of the seven parts of our task are complete. You have made it through + * the Bit of Despair (I think that's somewhere in the page table code, + * myself). + * + * Next, we examine "make Switcher". It's short, but intense. + */ diff --git a/drivers/lguest/switcher.S b/drivers/lguest/switcher.S new file mode 100644 index 00000000000..7c9c230cc84 --- /dev/null +++ b/drivers/lguest/switcher.S @@ -0,0 +1,350 @@ +/*P:900 This is the Switcher: code which sits at 0xFFC00000 to do the low-level + * Guest<->Host switch. It is as simple as it can be made, but it's naturally + * very specific to x86. + * + * You have now completed Preparation. If this has whet your appetite; if you + * are feeling invigorated and refreshed then the next, more challenging stage + * can be found in "make Guest". :*/ + +/*S:100 + * Welcome to the Switcher itself! + * + * This file contains the low-level code which changes the CPU to run the Guest + * code, and returns to the Host when something happens. Understand this, and + * you understand the heart of our journey. + * + * Because this is in assembler rather than C, our tale switches from prose to + * verse. First I tried limericks: + * + * There once was an eax reg, + * To which our pointer was fed, + * It needed an add, + * Which asm-offsets.h had + * But this limerick is hurting my head. + * + * Next I tried haikus, but fitting the required reference to the seasons in + * every stanza was quickly becoming tiresome: + * + * The %eax reg + * Holds "struct lguest_pages" now: + * Cherry blossoms fall. + * + * Then I started with Heroic Verse, but the rhyming requirement leeched away + * the content density and led to some uniquely awful oblique rhymes: + * + * These constants are coming from struct offsets + * For use within the asm switcher text. + * + * Finally, I settled for something between heroic hexameter, and normal prose + * with inappropriate linebreaks. Anyway, it aint no Shakespeare. + */ + +// Not all kernel headers work from assembler +// But these ones are needed: the ENTRY() define +// And constants extracted from struct offsets +// To avoid magic numbers and breakage: +// Should they change the compiler can't save us +// Down here in the depths of assembler code. +#include <linux/linkage.h> +#include <asm/asm-offsets.h> +#include <asm/page.h> +#include "lg.h" + +// We mark the start of the code to copy +// It's placed in .text tho it's never run here +// You'll see the trick macro at the end +// Which interleaves data and text to effect. +.text +ENTRY(start_switcher_text) + +// When we reach switch_to_guest we have just left +// The safe and comforting shores of C code +// %eax has the "struct lguest_pages" to use +// Where we save state and still see it from the Guest +// And %ebx holds the Guest shadow pagetable: +// Once set we have truly left Host behind. +ENTRY(switch_to_guest) + // We told gcc all its regs could fade, + // Clobbered by our journey into the Guest + // We could have saved them, if we tried + // But time is our master and cycles count. + + // Segment registers must be saved for the Host + // We push them on the Host stack for later + pushl %es + pushl %ds + pushl %gs + pushl %fs + // But the compiler is fickle, and heeds + // No warning of %ebp clobbers + // When frame pointers are used. That register + // Must be saved and restored or chaos strikes. + pushl %ebp + // The Host's stack is done, now save it away + // In our "struct lguest_pages" at offset + // Distilled into asm-offsets.h + movl %esp, LGUEST_PAGES_host_sp(%eax) + + // All saved and there's now five steps before us: + // Stack, GDT, IDT, TSS + // And last of all the page tables are flipped. + + // Yet beware that our stack pointer must be + // Always valid lest an NMI hits + // %edx does the duty here as we juggle + // %eax is lguest_pages: our stack lies within. + movl %eax, %edx + addl $LGUEST_PAGES_regs, %edx + movl %edx, %esp + + // The Guest's GDT we so carefully + // Placed in the "struct lguest_pages" before + lgdt LGUEST_PAGES_guest_gdt_desc(%eax) + + // The Guest's IDT we did partially + // Move to the "struct lguest_pages" as well. + lidt LGUEST_PAGES_guest_idt_desc(%eax) + + // The TSS entry which controls traps + // Must be loaded up with "ltr" now: + // For after we switch over our page tables + // It (as the rest) will be writable no more. + // (The GDT entry TSS needs + // Changes type when we load it: damn Intel!) + movl $(GDT_ENTRY_TSS*8), %edx + ltr %dx + + // Look back now, before we take this last step! + // The Host's TSS entry was also marked used; + // Let's clear it again, ere we return. + // The GDT descriptor of the Host + // Points to the table after two "size" bytes + movl (LGUEST_PAGES_host_gdt_desc+2)(%eax), %edx + // Clear the type field of "used" (byte 5, bit 2) + andb $0xFD, (GDT_ENTRY_TSS*8 + 5)(%edx) + + // Once our page table's switched, the Guest is live! + // The Host fades as we run this final step. + // Our "struct lguest_pages" is now read-only. + movl %ebx, %cr3 + + // The page table change did one tricky thing: + // The Guest's register page has been mapped + // Writable onto our %esp (stack) -- + // We can simply pop off all Guest regs. + popl %ebx + popl %ecx + popl %edx + popl %esi + popl %edi + popl %ebp + popl %gs + popl %eax + popl %fs + popl %ds + popl %es + + // Near the base of the stack lurk two strange fields + // Which we fill as we exit the Guest + // These are the trap number and its error + // We can simply step past them on our way. + addl $8, %esp + + // The last five stack slots hold return address + // And everything needed to change privilege + // Into the Guest privilege level of 1, + // And the stack where the Guest had last left it. + // Interrupts are turned back on: we are Guest. + iret + +// There are two paths where we switch to the Host +// So we put the routine in a macro. +// We are on our way home, back to the Host +// Interrupted out of the Guest, we come here. +#define SWITCH_TO_HOST \ + /* We save the Guest state: all registers first \ + * Laid out just as "struct lguest_regs" defines */ \ + pushl %es; \ + pushl %ds; \ + pushl %fs; \ + pushl %eax; \ + pushl %gs; \ + pushl %ebp; \ + pushl %edi; \ + pushl %esi; \ + pushl %edx; \ + pushl %ecx; \ + pushl %ebx; \ + /* Our stack and our code are using segments \ + * Set in the TSS and IDT \ + * Yet if we were to touch data we'd use \ + * Whatever data segment the Guest had. \ + * Load the lguest ds segment for now. */ \ + movl $(LGUEST_DS), %eax; \ + movl %eax, %ds; \ + /* So where are we? Which CPU, which struct? \ + * The stack is our clue: our TSS starts \ + * It at the end of "struct lguest_pages". \ + * Or we may have stumbled while restoring \ + * Our Guest segment regs while in switch_to_guest, \ + * The fault pushed atop that part-unwound stack. \ + * If we round the stack down to the page start \ + * We're at the start of "struct lguest_pages". */ \ + movl %esp, %eax; \ + andl $(~(1 << PAGE_SHIFT - 1)), %eax; \ + /* Save our trap number: the switch will obscure it \ + * (The Guest regs are not mapped here in the Host) \ + * %ebx holds it safe for deliver_to_host */ \ + movl LGUEST_PAGES_regs_trapnum(%eax), %ebx; \ + /* The Host GDT, IDT and stack! \ + * All these lie safely hidden from the Guest: \ + * We must return to the Host page tables \ + * (Hence that was saved in struct lguest_pages) */ \ + movl LGUEST_PAGES_host_cr3(%eax), %edx; \ + movl %edx, %cr3; \ + /* As before, when we looked back at the Host \ + * As we left and marked TSS unused \ + * So must we now for the Guest left behind. */ \ + andb $0xFD, (LGUEST_PAGES_guest_gdt+GDT_ENTRY_TSS*8+5)(%eax); \ + /* Switch to Host's GDT, IDT. */ \ + lgdt LGUEST_PAGES_host_gdt_desc(%eax); \ + lidt LGUEST_PAGES_host_idt_desc(%eax); \ + /* Restore the Host's stack where it's saved regs lie */ \ + movl LGUEST_PAGES_host_sp(%eax), %esp; \ + /* Last the TSS: our Host is complete */ \ + movl $(GDT_ENTRY_TSS*8), %edx; \ + ltr %dx; \ + /* Restore now the regs saved right at the first. */ \ + popl %ebp; \ + popl %fs; \ + popl %gs; \ + popl %ds; \ + popl %es + +// Here's where we come when the Guest has just trapped: +// (Which trap we'll see has been pushed on the stack). +// We need only switch back, and the Host will decode +// Why we came home, and what needs to be done. +return_to_host: + SWITCH_TO_HOST + iret + +// An interrupt, with some cause external +// Has ajerked us rudely from the Guest's code +// Again we must return home to the Host +deliver_to_host: + SWITCH_TO_HOST + // But now we must go home via that place + // Where that interrupt was supposed to go + // Had we not been ensconced, running the Guest. + // Here we see the cleverness of our stack: + // The Host stack is formed like an interrupt + // With EIP, CS and EFLAGS layered. + // Interrupt handlers end with "iret" + // And that will take us home at long long last. + + // But first we must find the handler to call! + // The IDT descriptor for the Host + // Has two bytes for size, and four for address: + // %edx will hold it for us for now. + movl (LGUEST_PAGES_host_idt_desc+2)(%eax), %edx + // We now know the table address we need, + // And saved the trap's number inside %ebx. + // Yet the pointer to the handler is smeared + // Across the bits of the table entry. + // What oracle can tell us how to extract + // From such a convoluted encoding? + // I consulted gcc, and it gave + // These instructions, which I gladly credit: + leal (%edx,%ebx,8), %eax + movzwl (%eax),%edx + movl 4(%eax), %eax + xorw %ax, %ax + orl %eax, %edx + // Now the address of the handler's in %edx + // We call it now: its "iret" takes us home. + jmp *%edx + +// Every interrupt can come to us here +// But we must truly tell each apart. +// They number two hundred and fifty six +// And each must land in a different spot, +// Push its number on stack, and join the stream. + +// And worse, a mere six of the traps stand apart +// And push on their stack an addition: +// An error number, thirty two bits long +// So we punish the other two fifty +// And make them push a zero so they match. + +// Yet two fifty six entries is long +// And all will look most the same as the last +// So we create a macro which can make +// As many entries as we need to fill. + +// Note the change to .data then .text: +// We plant the address of each entry +// Into a (data) table for the Host +// To know where each Guest interrupt should go. +.macro IRQ_STUB N TARGET + .data; .long 1f; .text; 1: + // Trap eight, ten through fourteen and seventeen + // Supply an error number. Else zero. + .if (\N <> 8) && (\N < 10 || \N > 14) && (\N <> 17) + pushl $0 + .endif + pushl $\N + jmp \TARGET + ALIGN +.endm + +// This macro creates numerous entries +// Using GAS macros which out-power C's. +.macro IRQ_STUBS FIRST LAST TARGET + irq=\FIRST + .rept \LAST-\FIRST+1 + IRQ_STUB irq \TARGET + irq=irq+1 + .endr +.endm + +// Here's the marker for our pointer table +// Laid in the data section just before +// Each macro places the address of code +// Forming an array: each one points to text +// Which handles interrupt in its turn. +.data +.global default_idt_entries +default_idt_entries: +.text + // The first two traps go straight back to the Host + IRQ_STUBS 0 1 return_to_host + // We'll say nothing, yet, about NMI + IRQ_STUB 2 handle_nmi + // Other traps also return to the Host + IRQ_STUBS 3 31 return_to_host + // All interrupts go via their handlers + IRQ_STUBS 32 127 deliver_to_host + // 'Cept system calls coming from userspace + // Are to go to the Guest, never the Host. + IRQ_STUB 128 return_to_host + IRQ_STUBS 129 255 deliver_to_host + +// The NMI, what a fabulous beast +// Which swoops in and stops us no matter that +// We're suspended between heaven and hell, +// (Or more likely between the Host and Guest) +// When in it comes! We are dazed and confused +// So we do the simplest thing which one can. +// Though we've pushed the trap number and zero +// We discard them, return, and hope we live. +handle_nmi: + addl $8, %esp + iret + +// We are done; all that's left is Mastery +// And "make Mastery" is a journey long +// Designed to make your fingers itch to code. + +// Here ends the text, the file and poem. +ENTRY(end_switcher_text) |