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[2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e2aad99f8sm25671645e9.17.2025.09.24.02.44.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 02:44:21 -0700 (PDT) Message-ID: <791e0d59-0eb2-481f-bf8b-ba4b413d5ebd@redhat.com> Date: Wed, 24 Sep 2025 11:44:19 +0200 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 Cc: Lance Yang , 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> <17dabd83-0849-44c9-b4a2-196af60d9676@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250924_024426_446734_7D576560 X-CRM114-Status: GOOD ( 20.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 24.09.25 11:34, Catalin Marinas wrote: > On Wed, Sep 24, 2025 at 11:13:18AM +0200, David Hildenbrand wrote: >> 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. > > Oh, which commit was this? It means that we can end up with > uninitialised tags if we have a PROT_MTE huge zero page since > set_pmd_at/set_pte_at() skips mte_sync_tags(). > This one: commit d82d09e482199e6bbc204df10b2082f764cbe1f4 Author: David Hildenbrand Date: Mon Aug 11 13:26:25 2025 +0200 mm/huge_memory: mark PMD mappings of the huge zero folio special The huge zero folio is refcounted (+mapcounted -- is that a word?) differently than "normal" folios, similarly (but different) to the ordinary shared zeropage. It should be in mm-stable, to go upstream in the upcoming merge window. It's been lurking in -next for a while now. As it behaves just like the ordinary shared zeropage now, would we have to zero/initialize the tags after allocating it? -- Cheers David / dhildenb