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imf19.hostedemail.com; dkim=none; spf=pass (imf19.hostedemail.com: domain of cmarinas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1758703811; a=rsa-sha256; cv=none; b=ToXmGgISLWp+KvmY8vEnHQ4U96w/62u8L11HSt+eArodArmUjpN7dQoCx8w41swgWhRHky a0RSZQtSNpvTTYJK7Zxh+OHl2BDuYVx9RKSl05prk1jurd1vL4LPx0C4rIGz1xmcJu6nfO HyxPIDuWW5Gl7a/O5+NzucdyXy3ynAY= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 91B4643CCC; Wed, 24 Sep 2025 08:50:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E087DC4CEE7; Wed, 24 Sep 2025 08:50:02 +0000 (UTC) Date: Wed, 24 Sep 2025 09:50:00 +0100 From: Catalin Marinas To: Lance Yang Cc: David Hildenbrand , 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 Subject: Re: [PATCH 1/1] mm/thp: fix MTE tag mismatch when replacing zero-filled subpages Message-ID: References: <20250922021458.68123-1-lance.yang@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 1EC5F1A000F X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: hdp7nfya8a3jjcfstxjz3ez9w9hqtexi X-HE-Tag: 1758703810-420660 X-HE-Meta: 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 zngqVoSg hE11YsrqXVYFmGgT4dwNOYwsYMiXxPautNzOE/ck1FYlZKgI5kM0bjugubNdysCdOlLNoLwy6GwPmSX6OYakcv4iKTdh9+FPV53Pg33EMpSuRvCMjrx5Ow+Ra3X6SItvDsBOUtkSyM+tUdXs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. If I go with the first fix for the page merging, I'll look to defer the zero page initialisation post page_alloc_init_late() in a separate patch. -- Catalin