migrate_pages/mempolicy semantics state that CAP_SYS_NICE is required
to move pages shared with another process to a different node.
page_mapcount > 1 is being used to determine if a hugetlb page is shared.
However, a hugetlb page will have a mapcount of 1 if mapped by multiple
processes via a shared PMD. As a result, hugetlb pages shared by multiple
processes and mapped with a shared PMD can be moved by a process without
CAP_SYS_NICE.
To fix, check for a shared PMD if mapcount is 1. If a shared PMD is
found consider the page shared.
Fixes: e2d8cf405525 ("migrate: add hugepage migration code to migrate_pages()")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/mempolicy.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 85a34f1f3ab8..72142fbe7652 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -600,7 +600,8 @@ static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,
/* With MPOL_MF_MOVE, we migrate only unshared hugepage. */
if (flags & (MPOL_MF_MOVE_ALL) ||
- (flags & MPOL_MF_MOVE && page_mapcount(page) == 1)) {
+ (flags & MPOL_MF_MOVE && page_mapcount(page) == 1 &&
+ !hugetlb_pmd_shared(pte))) {
if (isolate_hugetlb(page, qp->pagelist) &&
(flags & MPOL_MF_STRICT))
/*
--
2.39.1
