diff options
Diffstat (limited to 'drivers/lguest/lguest_asm.S')
| -rw-r--r-- | drivers/lguest/lguest_asm.S | 93 |
1 files changed, 0 insertions, 93 deletions
diff --git a/drivers/lguest/lguest_asm.S b/drivers/lguest/lguest_asm.S deleted file mode 100644 index 1ddcd5cd20f..00000000000 --- a/drivers/lguest/lguest_asm.S +++ /dev/null @@ -1,93 +0,0 @@ -#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: |