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 when migration completes.
Signed-off-by: Mel Gorman <[email protected]> --- mm/migrate.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/migrate.c b/mm/migrate.c index f78ec9b..f59b5de 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -146,7 +146,9 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma, pte = pte_mkold(mk_pte(new, vma->vm_page_prot)); if (pte_swp_soft_dirty(*ptep)) pte = pte_mksoft_dirty(pte); - if (is_write_migration_entry(entry)) + + /* Recheck VMA as permissions can change during migration started */ + if (is_write_migration_entry(entry) && (vma->vm_flags & (VM_WRITE))) pte = pte_mkwrite(pte); #ifdef CONFIG_HUGETLB_PAGE if (PageHuge(new)) { -- 1.8.4.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
