From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E1E82DBF73; Wed, 24 Sep 2025 10:02:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758708134; cv=none; b=Y9HBtKsFYsb+RUZjOoMFY23XU95Q4e5gHZ+Fw0De0B+TTUhxkBPvobnawM7vFOgvjFhdrlPAozyWGvGB9HF0nI2nr3jWSaVMH7sIRyC1DiNJX7qFy287T3pB5U8PgP+bbI3ksMalL8Q+JUSs99O5Iczxsa46Hxv4Y09ddnfJ11c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758708134; c=relaxed/simple; bh=YV83d5P+swyKnsGwmGnZHWOibOGSsH0UvCNy1qVyH/Y=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mhpQY/+BWSlhkk5EPQ17faDuNVde6Z5VblZFWJ0NJqEbOQKUXp4BbFSWGqlExvpDT/vtUQ8wzLHA1FwP6mp3v0KUpH48ZXndWznnBqr/hpHlWtHp8Gf1G85ZBI+0AeYZbzLTXiS4L3JjqXUXEWQD9u+maMFYfmkGr80pGAzCczY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id A36D5C4CEE7; Wed, 24 Sep 2025 09:59:49 +0000 (UTC) Date: Wed, 24 Sep 2025 10:59:23 +0100 From: Catalin Marinas To: David Hildenbrand 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 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> <17dabd83-0849-44c9-b4a2-196af60d9676@redhat.com> <791e0d59-0eb2-481f-bf8b-ba4b413d5ebd@redhat.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <791e0d59-0eb2-481f-bf8b-ba4b413d5ebd@redhat.com> On Wed, Sep 24, 2025 at 11:44:19AM +0200, David Hildenbrand wrote: > 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. Thanks. At least it's something to address in the next kernel version. I need to improve the MTE kselftests to catch the zero page scenarios. > As it behaves just like the ordinary shared zeropage now, would we have to > zero/initialize the tags after allocating it? Yes. Before pmd_special(), it was be done lazily via set_pmd_at(). I think it just needs a __GFP_ZEROTAGS. The only other place we use this flag is in vma_alloc_zeroed_movable_folio(), as an optimisation to avoid a separate loop for zeroing the tags after data. -- Catalin