3.16-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mel Gorman <mgor...@suse.de>
commit d3cb8bf6081b8b7a2dabb1264fe968fd870fa595 upstream.
A migration entry is marked as write if pte_write was true at the time the
entry was created. The VMA protections are not double checked when migration
entries are being removed as mprotect marks write-migration-entries as
read. It means that potentially we take a spurious fault to mark PTEs write
again but it's straight-forward. However, there is a race between write
migrations being marked read and migrations finishing. This potentially
allows a PTE to be write that should have been read. Close this race by
double checking the VMA permissions using maybe_mkwrite when migration
completes.
[torva...@linux-foundation.org: use maybe_mkwrite]
Signed-off-by: Mel Gorman <mgor...@suse.de>
Acked-by: Rik van Riel <r...@redhat.com>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
mm/migrate.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -146,8 +146,11 @@ static int remove_migration_pte(struct p
pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
if (pte_swp_soft_dirty(*ptep))
pte = pte_mksoft_dirty(pte);
+
+ /* Recheck VMA as permissions can change since migration started */
if (is_write_migration_entry(entry))
- pte = pte_mkwrite(pte);
+ pte = maybe_mkwrite(pte, vma);
+
#ifdef CONFIG_HUGETLB_PAGE
if (PageHuge(new)) {
pte = pte_mkhuge(pte);
--
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