mm/rmap: batch unmap file folios belonging to uffd-wp VMAs

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

Now that cond_install_uffd_wp_ptes() supports batching, call it with the
full batch length and allow folio_unmap_pte_batch() to batch file folios
belonging to uffd-wp VMAs.

For file folios, if the uffd-wp bit is set, unmapping converts present
PTEs into uffd-wp markers.  We must ensure that the same PTE range is not
reprocessed by the try_to_unmap_one() loop.

The page_vma_mapped_walk API ensures this: check_pte() only returns true
if any PFN in [pvmw->pfn, pvmw->pfn + nr_pages) is mapped by the PTE. 
There is no PFN underlying a uffd-wp marker PTE, so check_pte() returns
false and the walk skips ahead until it reaches a present entry again.

Link: https://lore.kernel.org/20260720065508.2695106-4-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 4 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index e6ffb63fe19b..1f72d279ba68 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_protected(vma))
-		return 1;
-
 	/*
 	 * If unmap fails, we need to restore the ptes. To avoid accidentally
 	 * upgrading write permissions for ptes that were not originally
@@ -2345,7 +2342,8 @@ 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.
 		 */
-		cond_install_uffd_wp_ptes(vma, address, pvmw.pte, pteval, 1);
+		cond_install_uffd_wp_ptes(vma, address, pvmw.pte, pteval,
+					  nr_pages);
 
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);