The quilt patch titled Subject: mm/rmap: fix potential out-of-bounds page table access during batched unmap has been removed from the -mm tree. Its filename was mm-rmap-fix-potential-out-of-bounds-page-table-access-during-batched-unmap.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------ From: Lance Yang lance.yang@linux.dev Subject: mm/rmap: fix potential out-of-bounds page table access during batched unmap Date: Fri, 27 Jun 2025 14:23:19 +0800

As pointed out by David[1], the batched unmap logic in try_to_unmap_one() may read past the end of a PTE table when a large folio's PTE mappings are not fully contained within a single page table.

While this scenario might be rare, an issue triggerable from userspace must be fixed regardless of its likelihood. This patch fixes the out-of-bounds access by refactoring the logic into a new helper, folio_unmap_pte_batch().

The new helper correctly calculates the safe batch size by capping the scan at both the VMA and PMD boundaries. To simplify the code, it also supports partial batching (i.e., any number of pages from 1 up to the calculated safe maximum), as there is no strong reason to special-case for fully mapped folios.

Link: https://lkml.kernel.org/r/20250701143100.6970-1-lance.yang@linux.dev Link: https://lkml.kernel.org/r/20250630011305.23754-1-lance.yang@linux.dev Link: https://lkml.kernel.org/r/20250627062319.84936-1-lance.yang@linux.dev Link: https://lore.kernel.org/linux-mm/a694398c-9f03-4737-81b9-7e49c857fcbe@redhat... [1] Fixes: 354dffd29575 ("mm: support batched unmap for lazyfree large folios during reclamation") Signed-off-by: Lance Yang lance.yang@linux.dev Suggested-by: David Hildenbrand david@redhat.com Reported-by: David Hildenbrand david@redhat.com Closes: https://lore.kernel.org/linux-mm/a694398c-9f03-4737-81b9-7e49c857fcbe@redhat... Suggested-by: Barry Song baohua@kernel.org Acked-by: Barry Song baohua@kernel.org Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Harry Yoo harry.yoo@oracle.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Chris Li chrisl@kernel.org Cc: "Huang, Ying" huang.ying.caritas@gmail.com Cc: Kairui Song kasong@tencent.com Cc: Lance Yang lance.yang@linux.dev Cc: Liam Howlett liam.howlett@oracle.com Cc: Mingzhe Yang mingzhe.yang@ly.com Cc: Rik van Riel riel@surriel.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: Tangquan Zheng zhengtangquan@oppo.com Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/rmap.c | 46 ++++++++++++++++++++++++++++------------------ 1 file changed, 28 insertions(+), 18 deletions(-)

--- a/mm/rmap.c~mm-rmap-fix-potential-out-of-bounds-page-table-access-during-batched-unmap +++ a/mm/rmap.c @@ -1845,23 +1845,32 @@ void folio_remove_rmap_pud(struct folio #endif }

-/* We support batch unmapping of PTEs for lazyfree large folios */ -static inline bool can_batch_unmap_folio_ptes(unsigned long addr, - struct folio *folio, pte_t *ptep) +static inline unsigned int folio_unmap_pte_batch(struct folio *folio, + struct page_vma_mapped_walk *pvmw, + enum ttu_flags flags, pte_t pte) { const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; - int max_nr = folio_nr_pages(folio); - pte_t pte = ptep_get(ptep); + unsigned long end_addr, addr = pvmw->address; + struct vm_area_struct *vma = pvmw->vma; + unsigned int max_nr; + + if (flags & TTU_HWPOISON) + return 1; + if (!folio_test_large(folio)) + return 1; + + /* We may only batch within a single VMA and a single page table. */ + end_addr = pmd_addr_end(addr, vma->vm_end); + max_nr = (end_addr - addr) >> PAGE_SHIFT;

+ /* We only support lazyfree batching for now ... */ if (!folio_test_anon(folio) || folio_test_swapbacked(folio)) - return false; + return 1; if (pte_unused(pte)) - return false; - if (pte_pfn(pte) != folio_pfn(folio)) - return false; + return 1;

- return folio_pte_batch(folio, addr, ptep, pte, max_nr, fpb_flags, NULL, - NULL, NULL) == max_nr; + return folio_pte_batch(folio, addr, pvmw->pte, pte, max_nr, fpb_flags, + NULL, NULL, NULL); }

/* @@ -2024,9 +2033,7 @@ static bool try_to_unmap_one(struct foli if (pte_dirty(pteval)) folio_mark_dirty(folio); } else if (likely(pte_present(pteval))) { - if (folio_test_large(folio) && !(flags & TTU_HWPOISON) && - can_batch_unmap_folio_ptes(address, folio, pvmw.pte)) - nr_pages = folio_nr_pages(folio); + nr_pages = folio_unmap_pte_batch(folio, &pvmw, flags, pteval); end_addr = address + nr_pages * PAGE_SIZE; flush_cache_range(vma, address, end_addr);

@@ -2206,13 +2213,16 @@ discard: hugetlb_remove_rmap(folio); } else { folio_remove_rmap_ptes(folio, subpage, nr_pages, vma); - folio_ref_sub(folio, nr_pages - 1); } if (vma->vm_flags & VM_LOCKED) mlock_drain_local(); - folio_put(folio); - /* We have already batched the entire folio */ - if (nr_pages > 1) + folio_put_refs(folio, nr_pages); + + /* + * If we are sure that we batched the entire folio and cleared + * all PTEs, we can just optimize and stop right here. + */ + if (nr_pages == folio_nr_pages(folio)) goto walk_done; continue; walk_abort: _

Patches currently in -mm which might be from lance.yang@linux.dev are

locking-rwsem-make-owner-helpers-globally-available.patch hung_task-extend-hung-task-blocker-tracking-to-rwsems.patch