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

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/[email protected]
Fixes: e2d8cf405525 ("migrate: add hugepage migration code to migrate_pages()")
Signed-off-by: Mike Kravetz <[email protected]>
Acked-by: Peter Xu <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: James Houghton <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Vishal Moola (Oracle) <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions