[PATCH 08/10] mm/hugetlb: tolerate UFFD_WP markers outside uffd-wp VMAs

["David Hildenbrand (Arm)" <david@kernel.org>]

UFFD PTE bit handling is a bit like swiss cheese, in particular with
recently added RWP mode. Having uffd-wp markers outside uffd-wp VMAs
already confused this code in the past and resulted in uffd-pte bits
confusing other code later.

Let's play safe and just ignore these markers in hugetlb_no_page(), not
silently propagating the uffd-wp PTE bit.

Fixes: 2d427bb01639 ("mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP")
Cc: stable@vger.kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/hugetlb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ba6860b9b7f4c..1548a6156206b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5939,8 +5939,11 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
 	/*
 	 * If this pte was previously wr-protected, keep it wr-protected even
 	 * if populated.
+	 *
+	 * TODO: fix all cases where uffd-wp markers remain in VMAs that are no
+	 * longer registered with uffd.
 	 */
-	if (unlikely(pte_is_uffd_wp_marker(vmf->orig_pte)))
+	if (unlikely(userfaultfd_wp(vma) && pte_is_uffd_wp_marker(vmf->orig_pte)))
 		new_pte = huge_pte_mkuffd(new_pte);
 	set_huge_pte_at(mm, vmf->address, vmf->pte, new_pte, huge_page_size(h));
 

-- 
2.43.0