[PATCH v2 5/9] mm/rmap: batch unmap folios belonging to uffd-wp VMAs

Dev Jain
2026-04-10T10:33:04Z

Commit a67fe41e214f ("mm: rmap: support batched unmapping for file large folios")
extended batched unmapping for file folios. That also required making
install_uffd_wp_ptes_if_needed() support batching, but that was left
out for the time being, and correctness was maintained by stopping
batching in case the VMA the folio belongs to is marked uffd-wp.

Now that we have a batched version called install_uffd_wp_ptes_if_needed,
simply call that. folio_unmap_pte_batch() ensures that the original state
of the ptes is either all uffd or all non-uffd, so we maintain
correctness.

If uffd-wp bit is there, we have the following transitions of ptes
after unmapping:

1) anon folio: present -> uffd-wp swap
2) file folio: present -> uffd-wp marker

We must ensure that these ptes are not reprocessed by the while loop -
if the batch length is less than the number of pages in the folio, then
we must skip over this batch.

The page_vma_mapped_walk API ensures this - check_pte() will return true
only if any of [pvmw->pfn, pvmw->pfn + nr_pages) is mapped by the pte.
There is no pfn underlying either a uffd-wp swap pte or a uffd-wp marker
pte, so check_pte returns false and we keep skipping until we hit a
present entry, which is where we want to batch from next.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
mm/rmap.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 20e1fb81c33fc..7a150edd96819 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1965,9 +1965,6 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio,
if (pte_unused(pte))
return 1;

- if (userfaultfd_wp(vma))
- return 1;
-
/*
* If unmap fails, we need to restore the ptes. To avoid accidentally
* upgrading write permissions for ptes that were not originally
@@ -2263,7 +2260,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
* we may want to replace a none pte with a marker pte if
* it's file-backed, so we don't lose the tracking info.
*/
- install_uffd_wp_ptes_if_needed(vma, address, pvmw.pte, pteval, 1);
+ install_uffd_wp_ptes_if_needed(vma, address, pvmw.pte, pteval, nr_pages);

/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
--
2.34.1