On 04/13/23 19:11, Peter Xu wrote:

When we try to unshare a pinned page for a private hugetlb, uffd-wp bit can get lost during unsharing. Fix it by carrying it over.

This should be very rare, only if an unsharing happened on a private hugetlb page with uffd-wp protected (e.g. in a child which shares the same page with parent with UFFD_FEATURE_EVENT_FORK enabled).

Cc: linux-stable stable@vger.kernel.org Fixes: 166f3ecc0daf ("mm/hugetlb: hook page faults for uffd write protection") Reported-by: Mike Kravetz mike.kravetz@oracle.com Signed-off-by: Peter Xu peterx@redhat.com

---

mm/hugetlb.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 7320e64aacc6..083aae35bff8 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5637,13 +5637,16 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, spin_lock(ptl); ptep = hugetlb_walk(vma, haddr, huge_page_size(h)); if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) {

• pte_t newpte = make_huge_pte(vma, &new_folio->page, !unshare);
  

• /* Break COW or unshare */ huge_ptep_clear_flush(vma, haddr, ptep); mmu_notifier_invalidate_range(mm, range.start, range.end); page_remove_rmap(old_page, vma, true); hugepage_add_new_anon_rmap(new_folio, vma, haddr);

• set_huge_pte_at(mm, haddr, ptep,
  

• 		make_huge_pte(vma, &new_folio->page, !unshare));
  

• if (huge_pte_uffd_wp(pte))
  

• 	newpte = huge_pte_mkuffd_wp(newpte);
  

• set_huge_pte_at(mm, haddr, ptep, newpte);
  

  folio_set_hugetlb_migratable(new_folio); /* Make the old page be freed below */ new_folio = page_folio(old_page);

-- 2.39.1

Thanks! Looks good,

Reviewed-by: Mike Kravetz mike.kravetz@oracle.com