From: Mel Gorman <mgorman@xxxxxxx> 3.4.105-rc1 review patch. If anyone has any objections, please let me know. ------------------ 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. [torvalds@xxxxxxxxxxxxxxxxxxxx: use maybe_mkwrite] Signed-off-by: Mel Gorman <mgorman@xxxxxxx> Acked-by: Rik van Riel <riel@xxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx> --- mm/migrate.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/migrate.c b/mm/migrate.c index 5f588b1..98b998f 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -139,8 +139,11 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma, get_page(new); pte = pte_mkold(mk_pte(new, vma->vm_page_prot)); + + /* 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); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html