The patch titled
Subject: mm/ksm: handle device-exclusive entries correctly in write_protect_page()
has been added to the -mm mm-unstable branch. Its filename is
mm-ksm-handle-device-exclusive-entries-correctly-in-write_protect_page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-ksm-handle-device-exclusive-entries-correctly-in-write_protect_page.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/ksm: handle device-exclusive entries correctly in write_protect_page()
Date: Mon, 10 Feb 2025 20:37:51 +0100
Ever since commit b756a3b5e7ea ("mm: device exclusive memory access") we
can return with a device-exclusive entry from page_vma_mapped_walk().
write_protect_page() 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, because GUP would never have returned such folios (conversion
to device-private happens by page migration, not in-place conversion of
the PTE).
There is a race between performing the folio_walk (which fails on
non-present PTEs) and locking the folio to look it up using
page_vma_mapped_walk() again, so this is likely a fix (unless something
else could prevent that race, but it doesn't look like). In the future it
could be handled if ever required, for now just give up and ignore them
like folio_walk would.
Link: https://lkml.kernel.org/r/20250210193801.781278-10-david@xxxxxxxxxx
Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Alex Shi <alexs@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Karol Herbst <kherbst@xxxxxxxxxx>
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Lyude <lyude@xxxxxxxxxx>
Cc: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Simona Vetter <simona.vetter@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yanteng Si <si.yanteng@xxxxxxxxx>
Cc: Barry Song <v-songbaohua@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/ksm.c~mm-ksm-handle-device-exclusive-entries-correctly-in-write_protect_page
+++ a/mm/ksm.c
@@ -1270,8 +1270,15 @@ static int write_protect_page(struct vm_
if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
goto out_unlock;
- anon_exclusive = PageAnonExclusive(&folio->page);
entry = ptep_get(pvmw.pte);
+ /*
+ * Handle PFN swap PTEs, such as device-exclusive ones, that actually
+ * map pages: give up just like the next folio_walk would.
+ */
+ if (unlikely(!pte_present(entry)))
+ goto out_unlock;
+
+ anon_exclusive = PageAnonExclusive(&folio->page);
if (pte_write(entry) || pte_dirty(entry) ||
anon_exclusive || mm_tlb_flush_pending(mm)) {
swapped = folio_test_swapcache(folio);
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-gup-reject-foll_split_pmd-with-hugetlb-vmas.patch
mm-rmap-reject-hugetlb-folios-in-folio_make_device_exclusive.patch
mm-rmap-convert-make_device_exclusive_range-to-make_device_exclusive.patch
mm-rmap-implement-make_device_exclusive-using-folio_walk-instead-of-rmap-walk.patch
mm-memory-detect-writability-in-restore_exclusive_pte-through-can_change_pte_writable.patch
mm-use-single-swp_device_exclusive-entry-type.patch
mm-page_vma_mapped-device-exclusive-entries-are-not-migration-entries.patch
kernel-events-uprobes-handle-device-exclusive-entries-correctly-in-__replace_page.patch
mm-ksm-handle-device-exclusive-entries-correctly-in-write_protect_page.patch
mm-rmap-handle-device-exclusive-entries-correctly-in-try_to_unmap_one.patch
mm-rmap-handle-device-exclusive-entries-correctly-in-try_to_migrate_one.patch
mm-rmap-handle-device-exclusive-entries-correctly-in-page_vma_mkclean_one.patch
mm-page_idle-handle-device-exclusive-entries-correctly-in-page_idle_clear_pte_refs_one.patch
mm-damon-handle-device-exclusive-entries-correctly-in-damon_folio_young_one.patch
mm-damon-handle-device-exclusive-entries-correctly-in-damon_folio_mkold_one.patch
mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries.patch
mm-rmap-avoid-ebusy-from-make_device_exclusive.patch
