Hi, this should fix bug https://bugzilla.kernel.org/show_bug.cgi?id=33682 . ==== Subject: thp: fix /dev/zero MAP_PRIVATE and vm_flags cleanups From: Andrea Arcangeli <aarcange@xxxxxxxxxx> The huge_memory.c THP page fault was allowed to run if vm_ops was null (which would succeed for /dev/zero MAP_PRIVATE, as the f_op->mmap wouldn't setup a special vma->vm_ops and it would fallback to regular anonymous memory) but other THP logics weren't fully activated for vmas with vm_file not NULL (/dev/zero has a not NULL vma->vm_file). So this removes the vm_file checks so that /dev/zero also can safely use THP (the other albeit safer approach to fix this bug would have been to prevent the THP initial page fault to run if vm_file was set). After removing the vm_file checks, this also makes huge_memory.c stricter in khugepaged for the DEBUG_VM=y case. It doesn't replace the vm_file check with a is_pfn_mapping check (but it keeps checking for VM_PFNMAP under VM_BUG_ON) because for a is_cow_mapping() mapping VM_PFNMAP should only be allowed to exist before the first page fault, and in turn when vma->anon_vma is null (so preventing khugepaged registration). So I tend to think the previous comment saying if vm_file was set, VM_PFNMAP might have been set and we could still be registered in khugepaged (despite anon_vma was not NULL to be registered in khugepaged) was too paranoid. The is_linear_pfn_mapping check is also I think superfluous (as described by comment) but under DEBUG_VM it is safe to stay. Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> --- diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index df29c8f..8847c8c 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -117,7 +117,7 @@ static inline void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long end, long adjust_next) { - if (!vma->anon_vma || vma->vm_ops || vma->vm_file) + if (!vma->anon_vma || vma->vm_ops) return; __vma_adjust_trans_huge(vma, start, end, adjust_next); } diff --git a/include/linux/mm.h b/include/linux/mm.h index 692dbae..2348db2 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -137,7 +137,8 @@ extern unsigned int kobjsize(const void *objp); #define VM_RandomReadHint(v) ((v)->vm_flags & VM_RAND_READ) /* - * special vmas that are non-mergable, non-mlock()able + * Special vmas that are non-mergable, non-mlock()able. + * Note: mm/huge_memory.c VM_NO_THP depends on this definition. */ #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 470dcda..83326ad 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1408,6 +1408,9 @@ out: return ret; } +#define VM_NO_THP (VM_SPECIAL|VM_INSERTPAGE|VM_MIXEDMAP|VM_SAO| \ + VM_HUGETLB|VM_SHARED|VM_MAYSHARE) + int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice) { @@ -1416,11 +1419,7 @@ int hugepage_madvise(struct vm_area_struct *vma, /* * Be somewhat over-protective like KSM for now! */ - if (*vm_flags & (VM_HUGEPAGE | - VM_SHARED | VM_MAYSHARE | - VM_PFNMAP | VM_IO | VM_DONTEXPAND | - VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE | - VM_MIXEDMAP | VM_SAO)) + if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP)) return -EINVAL; *vm_flags &= ~VM_NOHUGEPAGE; *vm_flags |= VM_HUGEPAGE; @@ -1436,11 +1435,7 @@ int hugepage_madvise(struct vm_area_struct *vma, /* * Be somewhat over-protective like KSM for now! */ - if (*vm_flags & (VM_NOHUGEPAGE | - VM_SHARED | VM_MAYSHARE | - VM_PFNMAP | VM_IO | VM_DONTEXPAND | - VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE | - VM_MIXEDMAP | VM_SAO)) + if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP)) return -EINVAL; *vm_flags &= ~VM_HUGEPAGE; *vm_flags |= VM_NOHUGEPAGE; @@ -1574,10 +1569,14 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma) * page fault if needed. */ return 0; - if (vma->vm_file || vma->vm_ops) + if (vma->vm_ops) /* khugepaged not yet working on file or special mappings */ return 0; - VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma)); + /* + * If is_pfn_mapping() is true is_learn_pfn_mapping() must be + * true too, verify it here. + */ + VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP); hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; hend = vma->vm_end & HPAGE_PMD_MASK; if (hstart < hend) @@ -1828,12 +1827,15 @@ static void collapse_huge_page(struct mm_struct *mm, (vma->vm_flags & VM_NOHUGEPAGE)) goto out; - /* VM_PFNMAP vmas may have vm_ops null but vm_file set */ - if (!vma->anon_vma || vma->vm_ops || vma->vm_file) + if (!vma->anon_vma || vma->vm_ops) goto out; if (is_vma_temporary_stack(vma)) goto out; - VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma)); + /* + * If is_pfn_mapping() is true is_learn_pfn_mapping() must be + * true too, verify it here. + */ + VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP); pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) @@ -2066,13 +2068,16 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, progress++; continue; } - /* VM_PFNMAP vmas may have vm_ops null but vm_file set */ - if (!vma->anon_vma || vma->vm_ops || vma->vm_file) + if (!vma->anon_vma || vma->vm_ops) goto skip; if (is_vma_temporary_stack(vma)) goto skip; - - VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma)); + /* + * If is_pfn_mapping() is true is_learn_pfn_mapping() + * must be true too, verify it here. + */ + VM_BUG_ON(is_linear_pfn_mapping(vma) || + vma->vm_flags & VM_NO_THP); hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; hend = vma->vm_end & HPAGE_PMD_MASK; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . 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