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mm: migrate: Close race between migration completion and mprotect

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commit d3cb8bf608 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@linux-foundation.org: use maybe_mkwrite]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>
This commit is contained in:
Mel Gorman 2014-10-02 19:47:41 +01:00 committed by Zefan Li
parent e5b741351f
commit ea38cd4170
1 changed files with 4 additions and 1 deletions
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5
mm/migrate.c
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@ -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);