The patch titled Subject: mm: pgtable: fix incorrect reclaim of non-empty PTE pages has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-pgtable-fix-incorrect-reclaim-of-non-empty-pte-pages.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: Qi Zheng zhengqi.arch@bytedance.com Subject: mm: pgtable: fix incorrect reclaim of non-empty PTE pages Date: Tue, 11 Feb 2025 15:26:25 +0800

In zap_pte_range(), if the pte lock was released midway, the pte entries may be refilled with physical pages by another thread, which may cause a non-empty PTE page to be reclaimed and eventually cause the system to crash.

To fix it, fall back to the slow path in this case to recheck if all pte entries are still none.

Link: https://lkml.kernel.org/r/20250211072625.89188-1-zhengqi.arch@bytedance.com Fixes: 6375e95f381e ("mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)") Signed-off-by: Qi Zheng zhengqi.arch@bytedance.com Reported-by: Christian Brauner brauner@kernel.org Closes: https://lore.kernel.org/all/20250207-anbot-bankfilialen-acce9d79a2c7@brauner... Reported-by: Qu Wenruo quwenruo.btrfs@gmx.com Closes: https://lore.kernel.org/all/152296f3-5c81-4a94-97f3-004108fba7be@gmx.com/ Tested-by: Zi Yan ziy@nvidia.com Cc: stable@vger.kernel.org Cc: "Darrick J. Wong" djwong@kernel.org Cc: Dave Chinner david@fromorbit.com Cc: David Hildenbrand david@redhat.com Cc: Jann Horn jannh@google.com Cc: Matthew Wilcox willy@infradead.org Cc: Muchun Song muchun.song@linux.dev Cc: Zi Yan ziy@nvidia.com Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)

--- a/mm/memory.c~mm-pgtable-fix-incorrect-reclaim-of-non-empty-pte-pages +++ a/mm/memory.c @@ -1719,7 +1719,7 @@ static unsigned long zap_pte_range(struc pmd_t pmdval; unsigned long start = addr; bool can_reclaim_pt = reclaim_pt_is_enabled(start, end, details); - bool direct_reclaim = false; + bool direct_reclaim = true; int nr;

retry: @@ -1734,8 +1734,10 @@ retry: do { bool any_skipped = false;

- if (need_resched()) + if (need_resched()) { + direct_reclaim = false; break; + }

nr = do_zap_pte_range(tlb, vma, pte, addr, end, details, rss, &force_flush, &force_break, &any_skipped); @@ -1743,11 +1745,20 @@ retry: can_reclaim_pt = false; if (unlikely(force_break)) { addr += nr * PAGE_SIZE; + direct_reclaim = false; break; } } while (pte += nr, addr += PAGE_SIZE * nr, addr != end);

- if (can_reclaim_pt && addr == end) + /* + * Fast path: try to hold the pmd lock and unmap the PTE page. + * + * If the pte lock was released midway (retry case), or if the attempt + * to hold the pmd lock failed, then we need to recheck all pte entries + * to ensure they are still none, thereby preventing the pte entries + * from being repopulated by another thread. + */ + if (can_reclaim_pt && direct_reclaim && addr == end) direct_reclaim = try_get_and_clear_pmd(mm, pmd, &pmdval);

add_mm_rss_vec(mm, rss); _

Patches currently in -mm which might be from zhengqi.arch@bytedance.com are

mm-pgtable-fix-incorrect-reclaim-of-non-empty-pte-pages.patch