mm/rmap: handle device-exclusive entries in folio_referenced_one()

page_vma_mapped_walk() can return non-present device-exclusive entries,
but folio_referenced_one() passes them to PTE young-bit accessors that
require present PTEs.

We must neither call clear_flush_young_ptes_notify() nor
folio_pte_batch() with non-present entries. For example, clearing the
young bit on non-present PTEs can corrupt the entry: on arm64
PTE_AF overlaps the swap type, so clearing it turns a device-exclusive
entry into an ordinary swap entry.

folio_pte_batch() will VM_WARN_ON_FOLIO.

Apply the same approach as the previous fixes to e.g., damon_ptep_mkold():
treat these entries as old from the CPU's perspective and obtain their
young state through the MMU notifier.

Skip PTE batching and MGLRU look-around for non-present entries, and
don't modify non-present PTEs.

Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: stable@vger.kernel.org
Reported-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Harry Yoo (Meta) <harry@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Link: https://patch.msgid.link/20261031-fixes_core-v3-9-d6437171ecc3@kernel.org
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

0 files changed, 0 insertions, 0 deletions