From 9348b73c2e1bfea74ccd4a44fb4ccc7276ab9623 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 9 Jan 2021 17:09:10 -0800 Subject: [PATCH] mm: don't play games with pinned pages in clear_page_refs Turning a pinned page read-only breaks the pinning after COW. Don't do it. The whole "track page soft dirty" state doesn't work with pinned pages anyway, since the page might be dirtied by the pinning entity without ever being noticed in the page tables. Signed-off-by: Linus Torvalds --- fs/proc/task_mmu.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index ab7d700..602e3a5 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1035,6 +1035,25 @@ struct clear_refs_private { }; #ifdef CONFIG_MEM_SOFT_DIRTY + +#define is_cow_mapping(flags) (((flags) & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE) + +static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr, pte_t pte) +{ + struct page *page; + + if (!pte_write(pte)) + return false; + if (!is_cow_mapping(vma->vm_flags)) + return false; + if (likely(!atomic_read(&vma->vm_mm->has_pinned))) + return false; + page = vm_normal_page(vma, addr, pte); + if (!page) + return false; + return page_maybe_dma_pinned(page); +} + static inline void clear_soft_dirty(struct vm_area_struct *vma, unsigned long addr, pte_t *pte) { @@ -1049,6 +1068,8 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma, if (pte_present(ptent)) { pte_t old_pte; + if (pte_is_pinned(vma, addr, ptent)) + return; old_pte = ptep_modify_prot_start(vma, addr, pte); ptent = pte_wrprotect(old_pte); ptent = pte_clear_soft_dirty(ptent); -- 2.7.4