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selftests/mm: fix uffd move-pmd test crash on 64K base page systems

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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: a2bf6a9ca8 ("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>
Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
Tested-by: Sarthak Sharma <sarthak.sharma@arm.com>
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>
This commit is contained in:
Zenghui Yu (Huawei) 2026-10-12 00:35:27 +08:00 committed by Andrew Morton
parent 1b0f9f70a3
commit 9f5c2aec33
1 changed files with 5 additions and 0 deletions
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5
tools/testing/selftests/mm/uffd-unit-tests.c
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@ -1937,6 +1937,11 @@ uffd_move_test_common(uffd_global_test_opts_t *gopts,
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");