openkylin
/
linux
mirror of https://gitee.com/openkylin/linux.git
9
0
Fork 0
Code Issues Projects Releases Wiki Activity

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: eef1b3ba05 ("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>
This commit is contained in:
Andrea Arcangeli 2016-08-25 15:16:57 -07:00 committed by Linus Torvalds
parent e7d316a02f
commit 804dd15046
1 changed files with 6 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
mm/huge_memory.c
View File

@ -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);