>From aacf36ad7b4bbe6d9f0afac83e8ca9b0666cb9f0 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 5 Aug 2014 11:33:59 +0100 Subject: [PATCH] x86,mm: fix pte_special versus pte_numa Sasha Levin has shown oopses on ffffea0003480048 and ffffea0003480008 at mm/memory.c:1132, running Trinity on different 3.16-rc-next kernels: where zap_pte_range() checks page->mapping to see if PageAnon(page). Those addresses fit struct pages for pfns d2001 and d2000, and in each dump a register or a stack slot showed d2001730 or d2000730: pte flags 0x730 are PCD ACCESSED PROTNONE SPECIAL IOMAP; and Sasha's e820 map has a hole between cfffffff and 100000000, which would need special access. Commit c46a7c817e66 ("x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels") has broken vm_normal_page(): a PROTNONE SPECIAL pte no longer passes the pte_special() test, so zap_pte_range() goes on to try to access a non-existent struct page. Fix this by refining pte_special() (SPECIAL with PRESENT or PROTNONE) to complement pte_numa() (SPECIAL with neither PRESENT nor PROTNONE). A hint that this was a problem was that c46a7c817e66 added pte_numa() test to vm_normal_page(), and moved its is_zero_pfn() test from slow to fast path: This was papering over a pte_special() snag when the zero page was encountered during zap. This patch reverts vm_normal_page() to how it was before, relying on pte_special(). It still appears that this patch may be incomplete: aren't there other places which need to be handling PROTNONE along with PRESENT? For example, pte_mknuma() clears _PAGE_PRESENT and sets _PAGE_NUMA, but on a PROT_NONE area, that would make it it pte_special(). This is side-stepped by the fact that NUMA hinting faults skiped PROT_NONE VMAs and there are no grounds where a NUMA hinting fault on a PROT_NONE VMA would be interesting. Partially-Fixes: c46a7c817e66 ("x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels") Reported-by: Sasha Levin Not-yet-Signed-off-by: Hugh Dickins Not-yet-Signed-off-by: Mel Gorman Cc: stable@vger.kernel.org [3.16] --- arch/x86/include/asm/pgtable.h | 9 +++++++-- mm/memory.c | 7 +++---- 2 files changed, 10 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 0ec0560..230b811 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -131,8 +131,13 @@ static inline int pte_exec(pte_t pte) static inline int pte_special(pte_t pte) { - return (pte_flags(pte) & (_PAGE_PRESENT|_PAGE_SPECIAL)) == - (_PAGE_PRESENT|_PAGE_SPECIAL); + /* + * See CONFIG_NUMA_BALANCING CONFIG_ARCH_USES_NUMA_PROT_NONE pte_numa() + * in include/asm-generic/pgtable.h: on x86 we have _PAGE_BIT_NUMA == + * _PAGE_BIT_GLOBAL+1 == __PAGE_BIT_SOFTW1 == _PAGE_BIT_SPECIAL. + */ + return (pte_flags(pte) & _PAGE_SPECIAL) && + (pte_flags(pte) & (_PAGE_PRESENT|_PAGE_PROTNONE)); } static inline unsigned long pte_pfn(pte_t pte) diff --git a/mm/memory.c b/mm/memory.c index 8b44f76..0a21f3d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -751,7 +751,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn = pte_pfn(pte); if (HAVE_PTE_SPECIAL) { - if (likely(!pte_special(pte) || pte_numa(pte))) + if (likely(!pte_special(pte))) goto check_pfn; if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) return NULL; @@ -777,15 +777,14 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, } } + if (is_zero_pfn(pfn)) + return NULL; check_pfn: if (unlikely(pfn > highest_memmap_pfn)) { print_bad_pte(vma, addr, pte, NULL); return NULL; } - if (is_zero_pfn(pfn)) - return NULL; - /* * NOTE! We still have PageReserved() pages in the page tables. * eg. VDSO mappings can cause them to exist.