+ selftests-mm-fix-uffd-move-pmd-test-crash-on-64k-base-page-systems.patch added to mm-new branch

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

The patch titled
     Subject: selftests/mm: fix uffd move-pmd test crash on 64K base page systems
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-fix-uffd-move-pmd-test-crash-on-64k-base-page-systems.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-fix-uffd-move-pmd-test-crash-on-64k-base-page-systems.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: "Zenghui Yu (Huawei)" <zenghui.yu@linux.dev>
Subject: selftests/mm: fix uffd move-pmd test crash on 64K base page systems
Date: Mon, 12 Oct 2026 00:35:27 +0800

uffd_move_pmd_test()/uffd_move_test_common() splits the test area into
chunks of chunk_size and moves them one by one.  On arm64 with 64K base
pages the chunk_size (read_pmd_pagesize()) is 512MB, which is larger than
the whole 32MB (UFFD_TEST_MEM_SIZE) test area:

  step_count = nr_pages / (chunk_size / page_size) == 0

Because chunk_size > page_size, the test then aligns both areas up to
512MB, which points far outside of the 32MB mappings, and decrements
step_count, which underflows to ULONG_MAX.  The verification loop then
runs away and the first dereference of area_src faults with a SIGSEGV.

Skip the test when a single chunk cannot fit into the test area.

Link: https://lore.kernel.org/20261011163527.95988-1-zenghui.yu@linux.dev
Fixes: a2bf6a9ca805 ("selftests/mm: add UFFDIO_MOVE ioctl test")
Signed-off-by: Zenghui Yu (Huawei) <zenghui.yu@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
---

 tools/testing/selftests/mm/uffd-unit-tests.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/tools/testing/selftests/mm/uffd-unit-tests.c~selftests-mm-fix-uffd-move-pmd-test-crash-on-64k-base-page-systems
+++ a/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -1937,6 +1937,11 @@ uffd_move_test_common(uffd_global_test_o
 
 	args.gopts = gopts;
 
+	if (chunk_size > gopts->nr_pages * gopts->page_size) {
+		uffd_test_skip("chunk size does not fit in the test area");
+		return;
+	}
+
 	/* Prevent source pages from being mapped more than once */
 	if (madvise(gopts->area_src, gopts->nr_pages * gopts->page_size, MADV_DONTFORK))
 		err("madvise(MADV_DONTFORK) failure");
_

Patches currently in -mm which might be from zenghui.yu@linux.dev are

selftests-damon-stop-kdamond-on-error-exits-of-no-op-commit-test.patch
selftests-damon-ignore-test-generated-damon_dump_output.patch
mm-damon-api-remove-unused-nr_damos_-enumerators.patch
selftests-mm-fix-uffd-move-pmd-test-crash-on-64k-base-page-systems.patch