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

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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/[email protected]
Fixes: e2d8cf4055 ("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]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Mike Kravetz 2023-01-26 14:27:21 -08:00 • committed by Greg Kroah-Hartman
commit a94695e0f9
1 changed files with 2 additions and 1 deletions
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3
mm/mempolicy.c
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@ -571,7 +571,8 @@ static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,
goto unlock;
/* 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)))
isolate_huge_page(page, qp->pagelist);
unlock:
spin_unlock(ptl);