From a8f97366452ed491d13cf1e44241bc0b5740b1f0 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Mon, 27 Nov 2017 06:21:25 +0300 Subject: [PATCH] mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d() Currently, we unconditionally make page table dirty in touch_pmd(). It may result in false-positive can_follow_write_pmd(). We may avoid the situation, if we would only make the page table entry dirty if caller asks for write access -- FOLL_WRITE. The patch also changes touch_pud() in the same way. Signed-off-by: Kirill A. Shutemov Cc: Michal Hocko Cc: Hugh Dickins Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 36 +++++++++++++----------------------- 1 file changed, 13 insertions(+), 23 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 86fe697e8bfb..0e7ded98d114 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -842,20 +842,15 @@ EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud); #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */ static void touch_pmd(struct vm_area_struct *vma, unsigned long addr, - pmd_t *pmd) + pmd_t *pmd, int flags) { pmd_t _pmd; - /* - * We should set the dirty bit only for FOLL_WRITE but for now - * the dirty bit in the pmd is meaningless. And if the dirty - * bit will become meaningful and we'll only set it with - * FOLL_WRITE, an atomic set_bit will be required on the pmd to - * set the young bit, instead of the current set_pmd_at. - */ - _pmd = pmd_mkyoung(pmd_mkdirty(*pmd)); + _pmd = pmd_mkyoung(*pmd); + if (flags & FOLL_WRITE) + _pmd = pmd_mkdirty(_pmd); if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK, - pmd, _pmd, 1)) + pmd, _pmd, flags & FOLL_WRITE)) update_mmu_cache_pmd(vma, addr, pmd); } @@ -884,7 +879,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, return NULL; if (flags & FOLL_TOUCH) - touch_pmd(vma, addr, pmd); + touch_pmd(vma, addr, pmd, flags); /* * device mapped pages can only be returned if the @@ -995,20 +990,15 @@ out: #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD static void touch_pud(struct vm_area_struct *vma, unsigned long addr, - pud_t *pud) + pud_t *pud, int flags) { pud_t _pud; - /* - * We should set the dirty bit only for FOLL_WRITE but for now - * the dirty bit in the pud is meaningless. And if the dirty - * bit will become meaningful and we'll only set it with - * FOLL_WRITE, an atomic set_bit will be required on the pud to - * set the young bit, instead of the current set_pud_at. - */ - _pud = pud_mkyoung(pud_mkdirty(*pud)); + _pud = pud_mkyoung(*pud); + if (flags & FOLL_WRITE) + _pud = pud_mkdirty(_pud); if (pudp_set_access_flags(vma, addr & HPAGE_PUD_MASK, - pud, _pud, 1)) + pud, _pud, flags & FOLL_WRITE)) update_mmu_cache_pud(vma, addr, pud); } @@ -1031,7 +1021,7 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, return NULL; if (flags & FOLL_TOUCH) - touch_pud(vma, addr, pud); + touch_pud(vma, addr, pud, flags); /* * device mapped pages can only be returned if the @@ -1424,7 +1414,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, page = pmd_page(*pmd); VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); if (flags & FOLL_TOUCH) - touch_pmd(vma, addr, pmd); + touch_pmd(vma, addr, pmd, flags); if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { /* * We don't mlock() pte-mapped THPs. This way we can avoid