From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-151.mta1.migadu.com [95.215.58.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DC5D03803D6 for ; Sat, 10 Oct 2026 08:36:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.151 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791621370; cv=none; b=R4MrlaV4dLkgDf3K+zzaQXIBz6YsumLo/qlkJm6OZGzHkt0mcyiaHeXnyEvs0E2sRjdDhTuFrYg8loNbQMZYI0x65ZYsCkhxbH/lTqU+G0pOHfWIvF/o7r2lA+hShWeHKpbuQlKGcju2oA9BtviLV6/Cj6UotRN6P6OlJ7s7Dck= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791621370; c=relaxed/simple; bh=/RC+izwEEYy8ZXvE6WOHCJ7ZNBYqaR8RFs6URHqTudY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LIEHJwfOLtCmd/wLQbGYuBVYE9Yt4N/AsvbDn8ag5OCoVn7Yi2Z2ndCYgRUVaR7/Z9yaokvBgQ41WRWor2Xan/YfD+/AxA7Ew2A3h3YUPlgUB/zYD8Io4e2uCMzGVpnX9FrgjObVug+rZjhmAyj1SPFM98jE46hU+BZKl1Sv3mg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=GedrZ0qo; arc=none smtp.client-ip=95.215.58.151 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="GedrZ0qo" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=/RC+izwEEYy8ZXvE6WOHCJ7ZNBYqaR8RFs6URHqTudY=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791621363; v=1; x=1792226163; b=GedrZ0qoPV7WD3EYE661u5OPJwvgyiOKYyTTetYQDCIYrEQJAmWjG86J2Ccyn27cx8B/qK+S 5QZUPWr1POkSxmS5F5xSQWVrZPtWWml34ngb9g2w+Wk5Oc1FzgNpVe1dUho9lSuSYcwDcGQoRP1 q0S2Wp/1ic5OBfC9uwfokt5w= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta10.migadu.com with ESMTPS id 765dd94070c37712; Sat, 10 Oct 2026 08:36:03 +0000 X-Mizu-Trace-ID: 765dd94070c37712 X-Migadu-Flow: FLOW_OUT Message-ID: <331b4e40-8d0c-4333-b2b6-b81e4c4b2e17@linux.dev> Date: Sat, 10 Oct 2026 16:35:53 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/compaction: skip folios containing hwpoisoned pages To: "David Hildenbrand (Arm)" , Yuanhe Shu , akpm@linux-foundation.org Cc: vbabka@kernel.org, linmiaohe@huawei.com, nao.horiguchi@gmail.com, ziy@nvidia.com, ying.huang@linux.alibaba.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: <20260928105805.1215770-1-xiangzao@linux.alibaba.com> <20260928105805.1215770-2-xiangzao@linux.alibaba.com> <99cbd960-439d-4672-aba9-6b49697db8b3@kernel.org> From: Kaitao Cheng In-Reply-To: <99cbd960-439d-4672-aba9-6b49697db8b3@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 在 2026/9/28 20:12, David Hildenbrand (Arm) 写道: > On 9/28/26 12:58, Yuanhe Shu wrote: >> memory_failure() sets PG_hwpoison on the error page before it manages >> to pin the folio via get_hwpoison_page(). Compaction running on >> another CPU can isolate that same folio in the meantime, so >> HWPoisonHandlable() then fails on !PageLRU(), the retry loop in >> get_any_page() exhausts itself and memory_failure() gives up with >> MF_IGNORED - while compaction still has the folio on its >> migratepages list, flagged PG_hwpoison. >> >> Nothing stops compaction from migrating such a folio afterwards. >> The corrupted data is copied into a fresh folio that carries no >> poison marker, and no hwpoison PTE entry is installed on the way >> back: the userspace mapping is silently redirected to the corrupted >> copy and no SIGBUS is ever delivered. >> >> Note that a large folio with a PG_hwpoisoned subpage can also sit on >> the LRU without any race at all, via the THP-split-failure path of >> memory_failure() (kill_procs_now() + MF_MSG_UNSPLIT_THP). Guarding >> compaction is therefore needed regardless of how the race in >> memory_failure() itself might be addressed. >> >> folio_mc_copy() does not close this hole: it only detects corruption >> at copy time and only where ARCH_HAS_COPY_MC is implemented (x86_64 >> and PPC64; elsewhere copy_mc_highpage() degrades to a plain copy). > > Then they should implement it. > >> Software-injected poison - what MADV_HWPOISON and the hwpoison-inject >> interface produce, and what tests and fuzzers exercise - never traps >> during the copy on any architecture. > > And these are debug interfaces, why do we care? > >> An isolation-time check avoids >> the migration entirely, on all architectures and for both real and >> simulated poison. > > It's racy. See the link below. Could we recheck PG_hwpoison on the source page after folio_mc_copy() completes, but before the mapping is transferred, and abort migration if the flag is set? This would prevent PG_hwpoison from being lost after migration. Completely closing the race window by modifying the arch-specific copy_mc_to_kernel() implementation would presumably also require corresponding hardware and architectural capabilities, which does not seem very practical. >> The check itself is two flag tests on the head page (PG_hwpoison >> and the folio-level has_hwpoisoned marker), not a walk over >> subpages. >> >> Neither page reclaim nor memory hotplug lets such a folio be >> copied into a fresh one: reclaim unmaps the poisoned order-0 page, >> and skips the hwpoisoned large folios it cannot safely unmap, in >> shrink_folio_list() >> commit 1b0449544c64 ("mm/vmscan: don't try to reclaim hwpoison folio") >> commit 9f1e8cd0b7c4 ("mm/vmscan: fix hwpoisoned large folio handling in shrink_folio_list") >> while memory hotplug refuses to migrate them in do_migrate_range() >> commit 5f5ee52d4f58 ("mm/hwpoison: introduce folio_contain_hwpoisoned_page() helper"). >> Skip them in compaction as well, for the same reason reclaim settled >> on skipping: the UCE is rare and a race with compaction is rarer >> still, so skipping is enough, and a later memory_failure() will >> handle the folio if the UCE is triggered again - while a migrated >> folio would silently propagate the corruption instead. >> >> Deterministic validation on v7.3-rc4-75-g62f4c998b297: order-4 >> mTHP folios were brought into the stable "large, on LRU, >> PG_hwpoisoned subpage" state by pinning a sibling subpage with >> vmsplice and injecting MADV_HWPOISON on another subpage, which >> makes memory_failure() take the THP-split-failure path; after >> triggering compaction, /proc/kpageflags shows which poisoned >> folios moved. The unpatched kernel migrated 16/16 poisoned >> folios and 16/16 clean controls in the same pageblocks; with >> this patch, 0/16 poisoned folios were migrated while their >> controls still migrated 16/16. > > > Was any of this written by an LLM? > >> >> Soft offline is not affected: it only sets the poison marker after >> its own migration has succeeded. >> >> Signed-off-by: Yuanhe Shu >> --- >> mm/compaction.c | 8 ++++++++ >> 1 file changed, 8 insertions(+) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index a049415512c6..491adcbc5313 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1093,6 +1093,14 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, >> if (unlikely(!folio)) >> goto isolate_fail; >> >> + /* >> + * Migrating would copy the corrupted data into a fresh >> + * folio with no poison marker; skip, as memory hotplug >> + * refuses to migrate such folios for the same reason. >> + */ >> + if (folio_contain_hwpoisoned_page(folio)) >> + goto isolate_fail_put; >> + >> /* >> * Migration will fail if an anonymous page is pinned in memory, >> * so avoid taking lru_lock and isolating it unnecessarily in an > > See > > https://lore.kernel.org/linux-mm/20260707090136.52904-1-kaitao.cheng@linux.dev/ > -- Thanks Kaitao Cheng