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Mon, 12 Oct 2026 05:12:10 -0700 (PDT) Received: from gmail.com ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48db9ac02cfsm18206754f8f.39.2026.10.12.05.12.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Oct 2026 05:12:09 -0700 (PDT) Date: Mon, 12 Oct 2026 14:12:07 +0200 From: "Jose A. Perez de Azpillaga" To: Zenghui Yu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, david@kernel.org, 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 Message-ID: References: <20261011163527.95988-1-zenghui.yu@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261011163527.95988-1-zenghui.yu@linux.dev> X-Rspamd-Queue-Id: E214920002 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: un7ifsupc3ws73687nywt89n1f5ibi4m X-HE-Tag: 1791807131-752543 X-HE-Meta: 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 c+fMUceK NLWb26bLwGVN9d/YCQFhDFN/nC/LALTh1e8L+mscE6YtTayHomSHnYVJC7qCkfdUltIUbjTfxUo8q7ZfpDjNBP9Q4znHuUllKwS98c61CFzE+zBZOoFTl1mAUuGcIwl/03Cebg6AGOdJfIfbdaZL1nS/Nmw0awrt/PvOhRdJkSJz+A8nvOhBzgeaZruFpBt5V2l/qnc0nX1munXTg2wCNSOR/Vt98WDxR3nDmQrr7ZNoCNVgkveysVWLhmxF3xdUgD5v3/hNmDsvxzhMquxuzA5VKCRNMMIfknEU8XSodbSME527EQTcHXDXI1nfsqF/FCdcvNCwR4qSabLrOqAdvSgMPboN4sTsH6dHA7FvwJcYUBR0aW8qE7IYBMkIw61JXqk43wYebIFjns2mkyMopF7Ko/kseDNBv1qyC Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 12, 2026 at 12:35:27AM +0800, Zenghui Yu wrote: > From: "Zenghui Yu (Huawei)" > > 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. > > Fixes: a2bf6a9ca805 ("selftests/mm: add UFFDIO_MOVE ioctl test") > Signed-off-by: Zenghui Yu (Huawei) > --- > tools/testing/selftests/mm/uffd-unit-tests.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c > index ef9b3956bdcf..2a97ba1d6feb 100644 > --- a/tools/testing/selftests/mm/uffd-unit-tests.c > +++ b/tools/testing/selftests/mm/uffd-unit-tests.c > @@ -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"); > -- > 2.53.0 > > LGTM. Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a