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[2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee15bfab67sm23593007f8f.43.2025.09.24.02.13.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 02:13:21 -0700 (PDT) Message-ID: <17dabd83-0849-44c9-b4a2-196af60d9676@redhat.com> Date: Wed, 24 Sep 2025 11:13:18 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/thp: fix MTE tag mismatch when replacing zero-filled subpages To: Catalin Marinas , Lance Yang Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, usamaarif642@gmail.com, yuzhao@google.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, voidice@gmail.com, Liam.Howlett@oracle.com, cerasuolodomenico@gmail.com, hannes@cmpxchg.org, kaleshsingh@google.com, npache@redhat.com, riel@surriel.com, roman.gushchin@linux.dev, rppt@kernel.org, ryan.roberts@arm.com, dev.jain@arm.com, ryncsn@gmail.com, shakeel.butt@linux.dev, surenb@google.com, hughd@google.com, willy@infradead.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, qun-wei.lin@mediatek.com, Andrew.Yang@mediatek.com, casper.li@mediatek.com, chinwen.chang@mediatek.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-mm@kvack.org, ioworker0@gmail.com, stable@vger.kernel.org References: <20250922021458.68123-1-lance.yang@linux.dev> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 24.09.25 10:50, Catalin Marinas wrote: > On Wed, Sep 24, 2025 at 10:49:27AM +0800, Lance Yang wrote: >> On 2025/9/24 00:14, Catalin Marinas wrote: >>> So alternative patch that also fixes the deferred struct page init (on >>> the assumptions that the zero page is always mapped as pte_special(): >> >> I can confirm that this alternative patch also works correctly; my tests >> for MTE all pass ;) > > Thanks Lance for testing. I'll post one of the variants today. > >> This looks like a better fix since it solves the boot hang issue too. > > In principle, yes, until I tracked down why I changed it in the first > place - 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to > the zero page"). ptrace() can read tags from PROT_MTE mappings and we > want to allow reading zeroes as well if the page points to the zero > page. Not flagging the page as PG_mte_tagged caused issues. > > I can change the logic in the ptrace() code, I just need to figure out > what happens to the huge zero page. Ideally we should treat both in the > same way but, AFAICT, we don't use pmd_mkspecial() on the huge zero > page, so it gets flagged with PG_mte_tagged. I changed that recently :) The huge zero folio will now always have pmd_special() set. -- Cheers David / dhildenb