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Thu, 29 Oct 2026 13:10:50 +0000 X-Mizu-Trace-ID: d29fc1ab4caede27 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Thu, 29 Oct 2026 21:10:42 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: fix uffd move-pmd test crash on 64K base page systems To: Sarthak Sharma 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 References: <20261011163527.95988-1-zenghui.yu@linux.dev> Content-Language: en-US From: Zenghui Yu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 8j4q5uzog9x5icfkynyttaitjyc6uod7 X-Spam-Status: No, score=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E92D5A0007 X-Rspam-User: X-HE-Tag: 1793279451-57052 X-HE-Meta: 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 oofudEJE nShg2XvR1YSASIOvWhXHDaGxYmz21DnJG69G9EXmd76zN9+nR/FXgDxZj0h0BeoOK+cPduk4LN//0pamzDlyq+GvwUAzpuwk5nBUdI0G01+3+sOQh35eU/Hz08BhlMjscMu3D4zeiuuZOtGgLV0lKPPCGMgEibOzEKhkRClOvFnz6sCg6w0DTMHRpS6lLHqON3Ec4H8Yv4otbk0llXXSMPibK+7ItEm5WiderOR8K9Wi/+OiZrdWzMtdCrQn2k1XNPkzA7vmX2xTSwtuFFzCqLQhWxuEPvSlUoEZI4mJC7DSqWkElLUwYz3OCzYdJ4n+dxNptYqrMuRqcjnc3Hspse+UlsWYzN8OoFNrD9Y2D7Z9a9xJc3IVRJPrSfydP6yjwf9aWBHWoAHIFBHk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi Sarthak, On 10/12/26 2:13 PM, Sarthak Sharma wrote: > Hi Zenghui! > > On 10/11/26 10:05 PM, 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) > > --- > > I run the test on a 64k kernel. Before the patch, a segmentation fault > occurred, which was fixed by the patch. So: > > Tested-by: Sarthak Sharma Thanks a lot! > Though Sashiko has a few nits [1] you might take a look at. > > [1] > https://sashiko.dev/#/patchset/20261011163527.95988-1-zenghui.yu%40linux.dev I think both of these comments are valid and worth fixing, but I don't have much bandwidth to work on them in the next few days. If you are interested, please feel free to fix them up and post the follow-up. I'm happy to review and test it. Thanks again, Zenghui