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![Andrea Arcangeli](/assets/img/avatar_default.png)
The pte_same check is reliable only if the swap entry remains pinned (by the page lock on swapcache). We've also to ensure the swapcache isn't removed before we take the lock as try_to_free_swap won't care about the page pin. One of the possible impacts of this patch is that a KSM-shared page can point to the anon_vma of another process, which could exit before the page is freed. This can leave a page with a pointer to a recycled anon_vma object, or worse, a pointer to something that is no longer an anon_vma. [riel@redhat.com: changelog help] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Hugh Dickins <hughd@google.com> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
145 lines
4 KiB
C
145 lines
4 KiB
C
#ifndef __LINUX_KSM_H
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#define __LINUX_KSM_H
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/*
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* Memory merging support.
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*
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* This code enables dynamic sharing of identical pages found in different
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* memory areas, even if they are not shared by fork().
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*/
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#include <linux/bitops.h>
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#include <linux/mm.h>
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#include <linux/pagemap.h>
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#include <linux/rmap.h>
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#include <linux/sched.h>
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struct stable_node;
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struct mem_cgroup;
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struct page *ksm_does_need_to_copy(struct page *page,
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struct vm_area_struct *vma, unsigned long address);
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#ifdef CONFIG_KSM
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int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
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unsigned long end, int advice, unsigned long *vm_flags);
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int __ksm_enter(struct mm_struct *mm);
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void __ksm_exit(struct mm_struct *mm);
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static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
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{
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if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
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return __ksm_enter(mm);
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return 0;
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}
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static inline void ksm_exit(struct mm_struct *mm)
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{
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if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
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__ksm_exit(mm);
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}
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/*
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* A KSM page is one of those write-protected "shared pages" or "merged pages"
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* which KSM maps into multiple mms, wherever identical anonymous page content
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* is found in VM_MERGEABLE vmas. It's a PageAnon page, pointing not to any
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* anon_vma, but to that page's node of the stable tree.
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*/
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static inline int PageKsm(struct page *page)
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{
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return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
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(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
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}
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static inline struct stable_node *page_stable_node(struct page *page)
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{
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return PageKsm(page) ? page_rmapping(page) : NULL;
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}
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static inline void set_page_stable_node(struct page *page,
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struct stable_node *stable_node)
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{
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page->mapping = (void *)stable_node +
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(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
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}
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/*
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* When do_swap_page() first faults in from swap what used to be a KSM page,
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* no problem, it will be assigned to this vma's anon_vma; but thereafter,
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* it might be faulted into a different anon_vma (or perhaps to a different
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* offset in the same anon_vma). do_swap_page() cannot do all the locking
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* needed to reconstitute a cross-anon_vma KSM page: for now it has to make
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* a copy, and leave remerging the pages to a later pass of ksmd.
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*
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* We'd like to make this conditional on vma->vm_flags & VM_MERGEABLE,
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* but what if the vma was unmerged while the page was swapped out?
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*/
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static inline int ksm_might_need_to_copy(struct page *page,
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struct vm_area_struct *vma, unsigned long address)
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{
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struct anon_vma *anon_vma = page_anon_vma(page);
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return anon_vma &&
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(anon_vma->root != vma->anon_vma->root ||
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page->index != linear_page_index(vma, address));
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}
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int page_referenced_ksm(struct page *page,
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struct mem_cgroup *memcg, unsigned long *vm_flags);
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int try_to_unmap_ksm(struct page *page, enum ttu_flags flags);
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int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
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struct vm_area_struct *, unsigned long, void *), void *arg);
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void ksm_migrate_page(struct page *newpage, struct page *oldpage);
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#else /* !CONFIG_KSM */
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static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
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{
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return 0;
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}
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static inline void ksm_exit(struct mm_struct *mm)
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{
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}
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static inline int PageKsm(struct page *page)
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{
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return 0;
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}
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#ifdef CONFIG_MMU
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static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
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unsigned long end, int advice, unsigned long *vm_flags)
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{
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return 0;
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}
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static inline int ksm_might_need_to_copy(struct page *page,
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struct vm_area_struct *vma, unsigned long address)
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{
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return 0;
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}
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static inline int page_referenced_ksm(struct page *page,
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struct mem_cgroup *memcg, unsigned long *vm_flags)
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{
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return 0;
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}
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static inline int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
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{
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return 0;
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}
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static inline int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page*,
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struct vm_area_struct *, unsigned long, void *), void *arg)
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{
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return 0;
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}
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static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
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{
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}
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#endif /* CONFIG_MMU */
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#endif /* !CONFIG_KSM */
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#endif /* __LINUX_KSM_H */
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