The patch titled Subject: mm: mmu_notifier: fix inconsistent memory between secondary MMU and host has been added to the -mm tree. Its filename is mm-mmu_notifier-fix-inconsistent-memory-between-secondary-mmu-and-host.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> Subject: mm: mmu_notifier: fix inconsistent memory between secondary MMU and host There is a bug in set_pte_at_notify() which always sets the pte to the new page before releasing the old page in the secondary MMU. At this time, the process will access on the new page, but the secondary MMU still access on the old page, the memory is inconsistent between them The below scenario shows the bug more clearly: at the beginning: *p = 0, and p is write-protected by KSM or shared with parent process CPU 0 CPU 1 write 1 to p to trigger COW, set_pte_at_notify will be called: *pte = new_page + W; /* The W bit of pte is set */ *p = 1; /* pte is valid, so no #PF */ return back to secondary MMU, then the secondary MMU read p, but get: *p == 0; /* * !!!!!! * the host has already set p to 1, but the secondary * MMU still get the old value 0 */ call mmu_notifier_change_pte to release old page in secondary MMU We can fix it by release old page first, then set the pte to the new page. Note, the new page will be firstly used in secondary MMU before it is mapped into the page table of the process, but this is safe because it is protected by the page table lock, there is no race to change the pte Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> Cc: Avi Kivity <avi@xxxxxxxxxx> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mmu_notifier.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN include/linux/mmu_notifier.h~mm-mmu_notifier-fix-inconsistent-memory-between-secondary-mmu-and-host include/linux/mmu_notifier.h --- a/include/linux/mmu_notifier.h~mm-mmu_notifier-fix-inconsistent-memory-between-secondary-mmu-and-host +++ a/include/linux/mmu_notifier.h @@ -317,8 +317,8 @@ static inline void mmu_notifier_mm_destr unsigned long ___address = __address; \ pte_t ___pte = __pte; \ \ - set_pte_at(___mm, ___address, __ptep, ___pte); \ mmu_notifier_change_pte(___mm, ___address, ___pte); \ + set_pte_at(___mm, ___address, __ptep, ___pte); \ }) #else /* CONFIG_MMU_NOTIFIER */ _ Patches currently in -mm which might be from xiaoguangrong@xxxxxxxxxxxxxxxxxx are linux-next.patch mm-mmu_notifier-fix-inconsistent-memory-between-secondary-mmu-and-host.patch thp-fix-the-count-of-thp_collapse_alloc.patch thp-remove-unnecessary-check-in-start_khugepaged.patch thp-move-khugepaged_mutex-out-of-khugepaged.patch thp-remove-unnecessary-khugepaged_thread-check.patch thp-remove-wake_up_interruptible-in-the-exit-path.patch thp-remove-some-code-depend-on-config_numa.patch thp-merge-page-pre-alloc-in-khugepaged_loop-into-khugepaged_do_scan.patch thp-release-page-in-page-pre-alloc-path.patch thp-introduce-khugepaged_prealloc_page-and-khugepaged_alloc_page.patch thp-remove-khugepaged_loop.patch thp-use-khugepaged_enabled-to-remove-duplicate-code.patch thp-remove-unnecessary-set_recommended_min_free_kbytes.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html