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t=1791891985; bh=+/tmAYlOAhFHx+eNdgdyJnJ6w70pbf6q57G4Ef/v6WA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bblOWDABuEdwp25mU++GNGhbXiuxg916E62Wf4957pUKGgr0htSYNpzQL4T1TiXD8 EgPU9HYh3SqjXL4ufnO5gc0V8LoSIFgrUjsKs+sc1L2CRFf9krf8IwkylMALxh1lM4 LgXEfw/iAYgiZeE0SbEDScGW3OfPVGqimnJfRmjOn3vIA/iCR7VkU8xl7flpJk1iMn wG9XHH5ClDDVQgvMVGMX8IEhfTiIzfaHE0QgVdqblW3kWbGDiRWA95IUny0ruRu9iD WQ52H/Ol0kulQ8vO115SbdHHXBTd/rsb5+F9a9dJs8OfLxoMYnkpYr7e3Djtfn/1i2 FKHYquSqWAw5A== Message-ID: <53c19885-bed1-48fa-b18e-953f7b1e5d87@kernel.org> Date: Tue, 13 Oct 2026 13:46:19 +0200 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: Mike Rapoport Cc: Zenghui Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, peterx@redhat.com, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com References: <20261011163527.95988-1-zenghui.yu@linux.dev> <67c30e4c-3576-4ded-a71f-b49075ed42e3@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: i56899badt185tgfkfb4wonqg5ciny7z X-Rspamd-Queue-Id: 804F2C0002 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1791891986-590325 X-HE-Meta: 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 ABFInOXC 687DBLHirQRxGtj5jBmXPnAt+/9CkQ/Q7Mny4UVtRfcINu66LjGMppyZJZYUYY4y/SJEvienSzsSiCMPcMAjL1mpK54Rvz84ruE13rS42405hkxmVaLLJHurgvUiZ8INqv9RcSm4RQaMxOK62tHOhWMqRufPjI4xrQt4/xHiszBbpyhL7bsT7PCoj4BWTnVAL8nDVhSYeLFFT7nZlGXy6OLSDPxmvQhX0anGv2EyNZvkUZVWcrzpYtJM8LnBtYyUBIbJzNyFFr/bpaao= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/13/26 12:33, Mike Rapoport wrote: > On Tue, Oct 13, 2026 at 09:39:54AM +0200, David Hildenbrand (Arm) wrote: >> On 10/11/26 18:35, 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. >> >> That leaves 64k untested, though? Why not adjust the chunk size accordingly? > > To test anything PMD on arm64 with 64k pages we need to adjust > UFFD_TEST_MEM_SIZE to have at least 4 pages, i.e 2G :) > > Maybe we want UFFD_TEST_MEM_SIZE to scale with the page size? That was my thought. If you have 64k you better also have plenty of memory :) -- Cheers, David