migrate: hugetlb: check for hugetlb shared PMD in node migration

commit 73bdf65ea74857d7fb2ec3067a3cec0e261b1462 upstream.

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.

Link: https://lkml.kernel.org/r/20230126222721.222195-3-mike.kravetz@oracle.com
Fixes: e0ad292e621b ("migrate: add hugepage migration code to migrate_pages()")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 02c8a712282f1146cd2aa901af7db3e42572cc70..f940395667c82f7beacbb0ac65e08107f3fe5ddb 100644 (file)
--- 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))
                        /*