Ever since commit b756a3b5e7ea ("mm: device exclusive memory access")
we can return with a device-exclusive entry from page_vma_mapped_walk().
page_vma_mkclean_one() is not prepared for that, so teach it about these
PFN swap PTEs. Note that device-private entries are so far not applicable
on that path, as we expect ZONE_DEVICE pages so far only in migration code
when it comes to the RMAP.
Note that we could currently only run into this case with
device-exclusive entries on THPs. We still adjust the mapcount on
conversion to device-exclusive; this makes the rmap walk
abort early for small folios, because we'll always have
!folio_mapped() with a single device-exclusive entry. We'll adjust the
mapcount logic once all page_vma_mapped_walk() users can properly
handle device-exclusive entries.
Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/rmap.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/mm/rmap.c b/mm/rmap.c
index 7c471c3ea64c4..7b737f0f68fb5 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1044,6 +1044,14 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
pte_t *pte = pvmw->pte;
pte_t entry = ptep_get(pte);
+ /*
+ * PFN swap PTEs, such as device-exclusive ones, that
+ * actually map pages are clean and not writable from a
+ * CPU perspective. The MMU notifier takes care of any
+ * device aspects.
+ */
+ if (!pte_present(entry))
+ continue;
if (!pte_dirty(entry) && !pte_write(entry))
continue;
--
2.48.1
