diff options
authorAndrea Arcangeli <aarcange@redhat.com>2016-08-25 15:16:57 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-08-26 17:39:35 -0700
commit804dd150468cfd920d92d4b3cf00536fedef3902 (patch)
parente7d316a02f683864a12389f8808570e37fb90aa3 (diff)
soft_dirty: fix soft_dirty during THP split
While adding proper userfaultfd_wp support with bits in pagetable and swap entry to avoid false positives WP userfaults through swap/fork/ KSM/etc, I've been adding a framework that mostly mirrors soft dirty. So I noticed in one place I had to add uffd_wp support to the pagetables that wasn't covered by soft_dirty and I think it should have. Example: in the THP migration code migrate_misplaced_transhuge_page() pmd_mkdirty is called unconditionally after mk_huge_pmd. entry = mk_huge_pmd(new_page, vma->vm_page_prot); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); That sets soft dirty too (it's a false positive for soft dirty, the soft dirty bit could be more finegrained and transfer the bit like uffd_wp will do.. pmd/pte_uffd_wp() enforces the invariant that when it's set pmd/pte_write is not set). However in the THP split there's no unconditional pmd_mkdirty after mk_huge_pmd and pte_swp_mksoft_dirty isn't called after the migration entry is created. The code sets the dirty bit in the struct page instead of setting it in the pagetable (which is fully equivalent as far as the real dirty bit is concerned, as the whole point of pagetable bits is to be eventually flushed out of to the page, but that is not equivalent for the soft-dirty bit that gets lost in translation). This was found by code review only and totally untested as I'm working to actually replace soft dirty and I don't have time to test potential soft dirty bugfixes as well :). Transfer the soft_dirty from pmd to pte during THP splits. This fix avoids losing the soft_dirty bit and avoids userland memory corruption in the checkpoint. Fixes: eef1b3ba053aa6 ("thp: implement split_huge_pmd()") Link: http://lkml.kernel.org/r/1471610515-30229-2-git-send-email-aarcange@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Pavel Emelyanov <xemul@virtuozzo.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 6 insertions, 1 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2373f0a7d340..2db2112aa31e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1512,7 +1512,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
struct page *page;
pgtable_t pgtable;
pmd_t _pmd;
- bool young, write, dirty;
+ bool young, write, dirty, soft_dirty;
unsigned long addr;
int i;
@@ -1546,6 +1546,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
write = pmd_write(*pmd);
young = pmd_young(*pmd);
dirty = pmd_dirty(*pmd);
+ soft_dirty = pmd_soft_dirty(*pmd);
pmdp_huge_split_prepare(vma, haddr, pmd);
pgtable = pgtable_trans_huge_withdraw(mm, pmd);
@@ -1562,6 +1563,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
swp_entry_t swp_entry;
swp_entry = make_migration_entry(page + i, write);
entry = swp_entry_to_pte(swp_entry);
+ if (soft_dirty)
+ entry = pte_swp_mksoft_dirty(entry);
} else {
entry = mk_pte(page + i, vma->vm_page_prot);
entry = maybe_mkwrite(entry, vma);
@@ -1569,6 +1572,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
entry = pte_wrprotect(entry);
if (!young)
entry = pte_mkold(entry);
+ if (soft_dirty)
+ entry = pte_mksoft_dirty(entry);
if (dirty)
SetPageDirty(page + i);