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b=EM2ykc2sM19KUh3ECVkSBtjYmF1T/YD422txRparDWpIGchUyfu0bytpEKHETTBr5 yUYEcTH1X3HLe+PqbcVI/+dICbEoRpmgiPWApitwbfuBy5hXFbYulC0VAXVJIy1Yi4 ChJaV9rq33xfDxawCarfPUAEmeYUekEgN2kvUBjhOm4lQF0f6p+BAl0Q+WLbNdbNf/ JPqIKWyFFZDCtb9qgI6o5h0tLF8FEKyLWtRMAlFanVX0Bg2OS0WWwL4vjgbJ4uB8as Zl/isFqpW7Z6FL3tOqgju/5R6d752QxK/jZ8kZhxr0mo1AhZumzVGMPIK1dU/M/UpW KIsD3dKSupsVg== Message-ID: <99cbd960-439d-4672-aba9-6b49697db8b3@kernel.org> Date: Mon, 28 Sep 2026 14:12:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/compaction: skip folios containing hwpoisoned pages To: 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, kaitao.cheng@linux.dev, 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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 6h1jcdikkocxtkqhfwn9b7myzkhbucz6 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A028BC0008 X-HE-Tag: 1790597572-415546 X-HE-Meta: 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 fHKxbh2U bkJ0Ej3d7lo+3rq3nPukqpj29ae3+O99VKRMJWQ7HyHdAcrofv0bfaYzd8+aHq5E9uF4H2RnUIptnbQ4fkaCQtqRfye/lg48kt8Un6e4HkMvwKc5QTi7VX/PnlEo/58OXzTFEe4D1DJJUzOo2jAdtzH2W/FsvO2oOG0OdjwpaCX5wSG2Jua2szMQ49j+I8SzVQ1f/OlipQiJi2iB5VXKqKDP2dca9qfqfLkmR1+EePqy465dubuY7M8K27mZR1R32QY3ILQrniQRl/yGQAfvvEqUOq/ro0szaQvZM+U2hcxqcYq7CnZHXsXwoqXzmYarYnsjivetyBWrLMdFVgVG4FWXrHyD/xD3fhdvyKTYA2NfvrVBZpbTHkFc+ASRWtwRVYwdf Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. > 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/ -- Cheers, David