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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=UiY0D2eS; 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 4F835606A33A for ; Mon, 26 Oct 2026 09:55:58 +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=UiY0D2eS Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAB9C1F01825; Mon, 26 Oct 2026 09:55:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793008558; bh=8im7+ey/5FnzNCNbzYMW8gbmtzOtcHIHPfyk276y0gU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=UiY0D2eS/zDLciz8jMBU34fZpk83Z6KVC2QwvXn96fSYJeb9d7w9P4RqoPp1v60UK fxFbKWz5eT29zmVk9M6+FSI305SzGr67lQYe4zWklHstJQp15SvEPvGugyfIpl/rvY CH7xq96IxVIiwp6WB96Ei1GnyegMhj6IWVAWMhOJE6uqByr0fpheeFAMt6zbv6OJqH fFAqttiuxUfty801NFhA7Xyu3ziO5woaA64HFjQM8WeonkhVM2asDMZc84TIIUcZ4Z xnHtQcnKnP3UEwLI3gDpnwsRp5j+i6t9q65vHiwXaiGoazVlMfX18dbEEx7cG72qUr l1B/QHQxRLAQQ== Message-ID: Date: Mon, 26 Oct 2026 10:55:48 +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] mm/highmem: refuse to copy hwpoisoned folios in the !copy_mc fallbacks To: Yuanhe Shu , akpm@linux-foundation.org Cc: "Huang, Ying" , Kaitao Cheng , vbabka@kernel.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, 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: <20261026025724.1430747-1-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 03:57, Yuanhe Shu wrote: > Where copy_mc_to_kernel is defined, copy_mc_user_highpage() and > copy_mc_highpage() stop at a hardware error during the copy, report > the not-copied bytes and queue the source page for memory_failure(). > The !copy_mc fallbacks return 0 after a plain copy instead. With > PG_hwpoison set while the data stays readable - software-injected > poison (MADV_HWPOISON, the debugfs corrupt-pfn injector) or a > transient hardware error - there is no fault to recover from: the > copy completes, the destination folio carries no poison marker, and > the poison is consumed silently, the same poison consumption > commit 841a8bfcbad9 ("mm: prevent poison consumption when splitting > THP") refused to risk on the split path. > > Check the source folio with folio_contain_hwpoisoned_page() in both > fallbacks and return PAGE_SIZE, the not-copied-bytes convention of > the real copy_mc paths, so the callers take their existing error > paths: the COW and fork paths fail with -EHWPOISON, KSM and > khugepaged abort, and folio_mc_copy() propagates to the migration > core, where this composes with the separate migration-side checks. > On archs with copy_mc this code does not compile. > > The check runs after the copy: a check before it would leave open > the window between itself and the copy. A flag set before or during > the copy is caught, whatever state the data is in. A late software > injection cannot have corrupted the completed copy, and a synchronous > hardware error takes an arch without copy_mc down at the access; the > residue no flag check, before or after, can catch is corruption whose > hardware report lands after the last check. Closing that would need > architecture support, as discussed. > > The fallbacks do not queue memory_failure() on refusal: the flag is > already set, and memory failure either knows about the page or has > abandoned it. There must be a way to shorten this description. > > Suggested-by: "Huang, Ying" > Suggested-by: Kaitao Cheng > Assisted-by: LLM > Signed-off-by: Yuanhe Shu > Link: https://lore.kernel.org/r/877bjowf9i.fsf@DESKTOP-5N7EMDA/ > --- > include/linux/highmem.h | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index d7aac9de1c8a..f90f0c6204a4 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -474,12 +474,21 @@ static inline int copy_mc_user_highpage(struct page *to, struct page *from, > unsigned long vaddr, struct vm_area_struct *vma) > { > copy_user_highpage(to, from, vaddr, vma); > + /* > + * The flag can be set while the copy runs, so check after it; > + * a flag landing later can no longer have corrupted this copy. > + */ > + if (folio_contain_hwpoisoned_page(page_folio(from))) > + return PAGE_SIZE; > return 0; > } > > static inline int copy_mc_highpage(struct page *to, struct page *from) > { > copy_highpage(to, from); > + /* Same reasoning as in copy_mc_user_highpage(). */ > + if (folio_contain_hwpoisoned_page(page_folio(from))) > + return PAGE_SIZE; > return 0; > } > #endif As I said in the other thread, how is copying data that was already poisoned (and might trigger another MCE) reasonable? I can understand why you would want to maintain the second check (although I do wonder about memory barriers ... hmmm). -- Cheers, David