diff options
| -rw-r--r-- | arch/x86/xen/mmu.c | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index aef7af92b28..1bca25f60ff 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -1463,6 +1463,119 @@ static int xen_pgd_alloc(struct mm_struct *mm) return ret; } +#ifdef CONFIG_X86_64 +static __initdata u64 __last_pgt_set_rw = 0; +static __initdata u64 __pgt_buf_start = 0; +static __initdata u64 __pgt_buf_end = 0; +static __initdata u64 __pgt_buf_top = 0; +/* + * As a consequence of the commit: + * + * commit 4b239f458c229de044d6905c2b0f9fe16ed9e01e + * Author: Yinghai Lu <yinghai@kernel.org> + * Date: Fri Dec 17 16:58:28 2010 -0800 + * + * x86-64, mm: Put early page table high + * + * at some point init_memory_mapping is going to reach the pagetable pages + * area and map those pages too (mapping them as normal memory that falls + * in the range of addresses passed to init_memory_mapping as argument). + * Some of those pages are already pagetable pages (they are in the range + * pgt_buf_start-pgt_buf_end) therefore they are going to be mapped RO and + * everything is fine. + * Some of these pages are not pagetable pages yet (they fall in the range + * pgt_buf_end-pgt_buf_top; for example the page at pgt_buf_end) so they + * are going to be mapped RW. When these pages become pagetable pages and + * are hooked into the pagetable, xen will find that the guest has already + * a RW mapping of them somewhere and fail the operation. + * The reason Xen requires pagetables to be RO is that the hypervisor needs + * to verify that the pagetables are valid before using them. The validation + * operations are called "pinning". + * + * In order to fix the issue we mark all the pages in the entire range + * pgt_buf_start-pgt_buf_top as RO, however when the pagetable allocation + * is completed only the range pgt_buf_start-pgt_buf_end is reserved by + * init_memory_mapping. Hence the kernel is going to crash as soon as one + * of the pages in the range pgt_buf_end-pgt_buf_top is reused (b/c those + * ranges are RO). + * + * For this reason, 'mark_rw_past_pgt' is introduced which is called _after_ + * the init_memory_mapping has completed (in a perfect world we would + * call this function from init_memory_mapping, but lets ignore that). + * + * Because we are called _after_ init_memory_mapping the pgt_buf_[start, + * end,top] have all changed to new values (b/c init_memory_mapping + * is called and setting up another new page-table). Hence, the first time + * we enter this function, we save away the pgt_buf_start value and update + * the pgt_buf_[end,top]. + * + * When we detect that the "old" pgt_buf_start through pgt_buf_end + * PFNs have been reserved (so memblock_x86_reserve_range has been called), + * we immediately set out to RW the "old" pgt_buf_end through pgt_buf_top. + * + * And then we update those "old" pgt_buf_[end|top] with the new ones + * so that we can redo this on the next pagetable. + */ +static __init void mark_rw_past_pgt(void) { + + if (pgt_buf_end > pgt_buf_start) { + u64 addr, size; + + /* Save it away. */ + if (!__pgt_buf_start) { + __pgt_buf_start = pgt_buf_start; + __pgt_buf_end = pgt_buf_end; + __pgt_buf_top = pgt_buf_top; + return; + } + /* If we get the range that starts at __pgt_buf_end that means + * the range is reserved, and that in 'init_memory_mapping' + * the 'memblock_x86_reserve_range' has been called with the + * outdated __pgt_buf_start, __pgt_buf_end (the "new" + * pgt_buf_[start|end|top] refer now to a new pagetable. + * Note: we are called _after_ the pgt_buf_[..] have been + * updated.*/ + + addr = memblock_x86_find_in_range_size(PFN_PHYS(__pgt_buf_start), + &size, PAGE_SIZE); + + /* Still not reserved, meaning 'memblock_x86_reserve_range' + * hasn't been called yet. Update the _end and _top.*/ + if (addr == PFN_PHYS(__pgt_buf_start)) { + __pgt_buf_end = pgt_buf_end; + __pgt_buf_top = pgt_buf_top; + return; + } + + /* OK, the area is reserved, meaning it is time for us to + * set RW for the old end->top PFNs. */ + + /* ..unless we had already done this. */ + if (__pgt_buf_end == __last_pgt_set_rw) + return; + + addr = PFN_PHYS(__pgt_buf_end); + + /* set as RW the rest */ + printk(KERN_DEBUG "xen: setting RW the range %llx - %llx\n", + PFN_PHYS(__pgt_buf_end), PFN_PHYS(__pgt_buf_top)); + + while (addr < PFN_PHYS(__pgt_buf_top)) { + make_lowmem_page_readwrite(__va(addr)); + addr += PAGE_SIZE; + } + /* And update everything so that we are ready for the next + * pagetable (the one created for regions past 4GB) */ + __last_pgt_set_rw = __pgt_buf_end; + __pgt_buf_start = pgt_buf_start; + __pgt_buf_end = pgt_buf_end; + __pgt_buf_top = pgt_buf_top; + } + return; +} +#else +static __init void mark_rw_past_pgt(void) { } +#endif static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd) { #ifdef CONFIG_X86_64 @@ -1489,6 +1602,14 @@ static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte) unsigned long pfn = pte_pfn(pte); /* + * A bit of optimization. We do not need to call the workaround + * when xen_set_pte_init is called with a PTE with 0 as PFN. + * That is b/c the pagetable at that point are just being populated + * with empty values and we can save some cycles by not calling + * the 'memblock' code.*/ + if (pfn) + mark_rw_past_pgt(); + /* * If the new pfn is within the range of the newly allocated * kernel pagetable, and it isn't being mapped into an * early_ioremap fixmap slot as a freshly allocated page, make sure @@ -1997,6 +2118,8 @@ __init void xen_ident_map_ISA(void) static __init void xen_post_allocator_init(void) { + mark_rw_past_pgt(); + #ifdef CONFIG_XEN_DEBUG pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte_debug); #endif |