From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Zenghui Yu <zenghui.yu@linux.dev>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com,
ljs@kernel.org, liam@infradead.org, vbabka@kernel.org,
surenb@google.com, mhocko@suse.com
Subject: Re: [PATCH] selftests/mm: fix uffd move-pmd test crash on 64K base page systems
Date: Tue, 13 Oct 2026 09:39:54 +0200 [thread overview]
Message-ID: <67c30e4c-3576-4ded-a71f-b49075ed42e3@kernel.org> (raw)
In-Reply-To: <20261011163527.95988-1-zenghui.yu@linux.dev>
On 10/11/26 18:35, Zenghui Yu wrote:
> From: "Zenghui Yu (Huawei)" <zenghui.yu@linux.dev>
>
> 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.
That leaves 64k untested, though? Why not adjust the chunk size accordingly?
--
Cheers,
David
next prev parent reply other threads:[~2026-10-13 7:40 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-11 16:35 [PATCH] selftests/mm: fix uffd move-pmd test crash on 64K base page systems Zenghui Yu
2026-10-12 6:13 ` Sarthak Sharma
2026-10-12 12:12 ` Jose A. Perez de Azpillaga
2026-10-13 7:39 ` David Hildenbrand (Arm) [this message]
2026-10-13 10:33 ` Mike Rapoport
2026-10-13 11:46 ` David Hildenbrand (Arm)
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