+ mm-synchronize-with-pte-table-reclaim-for-all-folio-sizes.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: synchronize with PTE table reclaim for all folio sizes
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-synchronize-with-pte-table-reclaim-for-all-folio-sizes.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-synchronize-with-pte-table-reclaim-for-all-folio-sizes.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Baolin Wang <baolin.wang@linux.alibaba.com>
Subject: mm: synchronize with PTE table reclaim for all folio sizes
Date: Thu, 05 Nov 2026 10:56:28 +0800

Similar to commit 243cf1f67b36 ("mm: memory: fix truncation removing
mapped folios"), the '!pmd_present()' check in page_vma_mapped_walk() can
also race with concurrent page table reclamation via
zap_empty_pte_table().

page_vma_mapped_walk() is used by many functions including try_to_unmap(),
try_to_migrate(), folio_mkclean(), pfn_mkclean_range(),
remove_migration_ptes(), page_mapped_in_vma(), and
mapping_wrprotect_range().  Except for try_to_unmap() and
try_to_migrate(), the other callers do not perform post-walk accounting
checks, so the race has no observable impact on them.

For migration, the race can cause unnecessary retries.  For reclaim via
try_to_unmap(), the race can cause failure to reclaim a folio that is in
fact already unmapped (as shown below), which may lead to unexpected OOM
or increased refaults.

CPU 0 (reclaim)                      CPU 1 (MADV_DONTNEED)
--------------------------------    --------------------------------
folio_lock(F)
try_to_unmap(F, TTU_SYNC)
                                    zap_pte_range(full PMD range)
                                      spin_lock(ptl)
                                      clear PTEs
                                      zap_empty_pte_table()
                                        spin_trylock(pml)
                                        pmd_clear()
                                        spin_unlock(pml)

  page_vma_mapped_walk()
    observe !pmd_present(pmde)
    nr_pages < HPAGE_PMD_NR
    skip synchronization
    return false

try_to_unmap() returns
folio_mapped(F) == true
nr_unmap_fail += folio_nr_pages(F)
                                    tlb_flush_mmu_tlbonly()
                                    tlb_flush_rmaps()
                                      remove F's rmaps
                                    spin_unlock(ptl)

Commit 243cf1f67b36 ("mm: memory: fix truncation removing mapped folios")
has already moved the PMD clear operation (via zap_empty_pte_table()) to
after tlb_flush_rmaps().  Similarly, page_vma_mapped_walk() also needs to
use sync_with_folio_pmd_zap() to synchronize and avoid memory ordering
issues on weakly ordered CPUs.

Link: https://lore.kernel.org/affd6da4e8d0de1424a4e0b3bafcd1324dfb6c97.1793847060.git.baolin.wang@linux.alibaba.com
Fixes: 6375e95f381e ("mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: <ayushr@modal.com>
Cc: <stable@vger.kernel.org>
---

 mm/page_vma_mapped.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

--- a/mm/page_vma_mapped.c~mm-synchronize-with-pte-table-reclaim-for-all-folio-sizes
+++ a/mm/page_vma_mapped.c
@@ -293,10 +293,7 @@ restart:
 			spin_unlock(pvmw->ptl);
 			pvmw->ptl = NULL;
 		} else if (!pmd_present(pmde)) {
-			if ((pvmw->flags & PVMW_SYNC) &&
-			    thp_vma_suitable_order(vma, pvmw->address,
-						   PMD_ORDER) &&
-			    (pvmw->nr_pages >= HPAGE_PMD_NR))
+			if (pvmw->flags & PVMW_SYNC)
 				sync_with_folio_pmd_zap(mm, pvmw->pmd);
 
 			goto next_pmd;
_

Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are

mm-synchronize-with-pte-table-reclaim-for-all-folio-sizes.patch