[merged mm-hotfixes-stable] mm-huge_memory-fix-folio-split-check-for-anon-folios-in-swapcache.patch removed from -mm tree

[merged mm-hotfixes-stable] mm-huge_memory-fix-folio-split-check-for-anon-folios-in-swapcache.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/huge_memory: fix folio split check for anon folios in swapcache
has been removed from the -mm tree.  Its filename was
     mm-huge_memory-fix-folio-split-check-for-anon-folios-in-swapcache.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: Zi Yan <ziy@nvidia.com>
Subject: mm/huge_memory: fix folio split check for anon folios in swapcache
Date: Wed, 5 Nov 2025 11:29:10 -0500

Both uniform and non uniform split check missed the check to prevent
splitting anon folios in swapcache to non-zero order.

Splitting anon folios in swapcache to non-zero order can cause data
corruption since swapcache only support PMD order and order-0 entries. 
This can happen when one use split_huge_pages under debugfs to split
anon folios in swapcache.

In-tree callers do not perform such an illegal operation.  Only debugfs
interface could trigger it.  I will put adding a test case on my TODO
list.

Fix the check.

Link: https://lkml.kernel.org/r/20251105162910.752266-1-ziy@nvidia.com
Fixes: 58729c04cf10 ("mm/huge_memory: add buddy allocator like (non-uniform) folio_split()")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reported-by: "David Hildenbrand (Red Hat)" <david@kernel.org>
Closes: https://lore.kernel.org/all/dc0ecc2c-4089-484f-917f-920fdca4c898@kernel.org/
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-fix-folio-split-check-for-anon-folios-in-swapcache
+++ a/mm/huge_memory.c
@@ -3522,7 +3522,8 @@ bool non_uniform_split_supported(struct
 		/* order-1 is not supported for anonymous THP. */
 		VM_WARN_ONCE(warns && new_order == 1,
 				"Cannot split to order-1 folio");
-		return new_order != 1;
+		if (new_order == 1)
+			return false;
 	} else if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
 	    !mapping_large_folio_support(folio->mapping)) {
 		/*
@@ -3553,7 +3554,8 @@ bool uniform_split_supported(struct foli
 	if (folio_test_anon(folio)) {
 		VM_WARN_ONCE(warns && new_order == 1,
 				"Cannot split to order-1 folio");
-		return new_order != 1;
+		if (new_order == 1)
+			return false;
 	} else  if (new_order) {
 		if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
 		    !mapping_large_folio_support(folio->mapping)) {
_

Patches currently in -mm which might be from ziy@nvidia.com are

mm-huge_memory-add-split_huge_page_to_order.patch
mm-memory-failure-improve-large-block-size-folio-handling.patch
mm-huge_memory-fix-kernel-doc-comments-for-folio_split-and-related.patch
mm-huge_memory-fix-kernel-doc-comments-for-folio_split-and-related-fix.patch
mm-huge_memory-fix-kernel-doc-comments-for-folio_split-and-related-fix-2.patch
migrate-optimise-alloc_migration_target-fix.patch