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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ADibYKa6; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DF022606A31A for ; Mon, 26 Oct 2026 09:57:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ADibYKa6 Received: by smtp.kernel.org (Postfix) with ESMTPSA id AFB981F01825; Mon, 26 Oct 2026 09:56:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793008622; bh=uEc1Bmciiva82nUX+FVCSYZVGtSGCp8Z+LUTT/EsGek=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ADibYKa6IDFelyxOrz8R24pUpYscXPB+pjFUqfN2yzvXXexfAjjlvE8xEfbuxib1a 9iuKKqlbVMsfHNfY8DCH1nNOgHe4kTajBG8upwqlZp9HUaz0Jm3ecdaV86Vb7/vNvQ pVTUkIJ1PrXGqNfuWJj4ilB87T5xg70/iei3rAqXx6qEUbMNQlQKTCvPCNx0BPsKu1 lpfZjxcbWshFPOnI+aAlGyoG1VN7lODhcoXGWlZH27/b+4YYdt8nqCAscjnoWTkJKj LVXMT/ryh3eVhd+NCWnLLVqiT4ue426VHLCP7J6ORkJwIvkzwPbZ4RahyvrSR2DIY2 D2GTiBGBSgRPg== Message-ID: <18602383-2326-4e54-8dec-bb695ae8878e@kernel.org> Date: Mon, 26 Oct 2026 10:56:55 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/2] mm: don't migrate folios containing hwpoisoned pages To: Yuanhe Shu , akpm@linux-foundation.org Cc: "Huang, Ying" , Kaitao Cheng , vbabka@kernel.org, linmiaohe@huawei.com, nao.horiguchi@gmail.com, ziy@nvidia.com, wangkefeng.wang@huawei.com, tujinjiang@huawei.com, mgorman@techsingularity.net, chengkaitao@kylinos.cn, muchun.song@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261026025552.1427901-1-xiangzao@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/26/26 03:55, Yuanhe Shu wrote: > v2 of this series. No changes to the approach; the two deltas are a > wording correction promised in the v1 discussion and a third check > suggested by Kaitao Cheng. > > memory_failure() can end up abandoning a folio while PG_hwpoison is > already set on it. Two ways to get there: > > 1. Race: any isolator (compaction, NUMA balancing, move_pages(), > mbind(), CMA, long-term GUP) clears PG_lru from under > memory_failure(), which then fails the HWPoisonHandlable() > check, exhausts the get_any_page() retries and bails out with > MF_IGNORED - without holding any reference, but with the flag > set. > > 2. No race at all: the THP-split-failure path > (kill_procs_now() + MF_MSG_UNSPLIT_THP) leaves a large folio > on the LRU with a PG_hwpoisoned subpage by design. > > In both cases the migrator still holds the folio on its migration > list and migrates it like any other: the corrupted data is copied > into a fresh folio with no poison marker, and no hwpoison PTE entry > is installed on the way back, so the userspace mapping is silently > redirected to the corrupted copy - no SIGBUS is ever delivered. > > This was reproduced on v7.3-rc4-75-g62f4c998b297 (the base of > this series): an order-0 stress workload (madvise(MADV_HWPOISON) > racing move_pages()) left the poison flag set on 8426 abandoned > folios in a 180-second run; 698 of them were subsequently > migrated, and in every case the address then served the copied > corrupted data with no SIGBUS. With patch 2, 0 of 9711 were > propagated. > > The compaction-side guard is needed regardless of how the race in > memory_failure() itself might be addressed: the steady state > (split failure leaves the folio on the LRU with the flag already > set) is not a race at all. Deterministically validated 16/16 > poisoned mTHP folios migrated unpatched vs 0/16 with patch 1, > with clean controls migrating 16/16 in both runs. > > The checks compose with, not replace, copy_mc: folio_mc_copy() > still catches real-DRAM corruption during the copy on archs that > implement it, and the flag checks refuse software-injected poison > on all archs before and after the copy. Extending the > !ARCH_HAS_COPY_MC fallbacks of copy_mc_user_highpage() and > copy_mc_highpage() with the same flag check - which would also > cover their non-migration callers - was proposed by Huang, Ying > and welcomed by David in the v1 discussion; that is posted as a > separate patch right after this series. With that patch in place, why do we still need these changes here? -- Cheers, David