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Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0XDjF4uj_1793272333 cluster:ay36) by smtp.aliyun-inc.com; Thu, 29 Oct 2026 19:12:19 +0800 From: "Huang, Ying" To: Yuanhe Shu Cc: akpm@linux-foundation.org, david@kernel.org, "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 Subject: Re: [PATCH v2] mm/highmem: refuse to copy hwpoisoned folios in the !copy_mc fallbacks In-Reply-To: <20261029034254.2487998-1-xiangzao@linux.alibaba.com> (Yuanhe Shu's message of "Thu, 29 Oct 2026 11:42:54 +0800") References: <20261029034254.2487998-1-xiangzao@linux.alibaba.com> Date: Thu, 29 Oct 2026 19:12:13 +0800 Message-ID: <87zevwiwvm.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Queue-Id: 77707C000A X-Stat-Signature: pnf8iaa1a963re76mq65c66rr5uwus9z X-Spam-Status: No, score=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793272344-463156 X-HE-Meta: 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 oIvBBj7F ObXhhiMFro+Wdql1po07O9NmkgPA2fRheaNQHMtAISeUmJ4EMOBPKmuOdgmIBlj31ZqwLWV0n6Jkg14gP+cGRchv5ULqbMkXLgBFl68PLtqjSdvlkH9Hb6v/bLD8ku4BYu5D8UjreSVYOatTuIs+0KJKRuDnXQrp7GVJRcz7lYdzYJ4fDdjMpgDuCdiO/x/Ie5797UjlbzfoWk3HJzEzI+pO2C9wfF22aSE5EJdmMuc7aW0Whm5n75Vz3nUsDKnuzYpEucb3+Y3fjadK9DmSUcv+CxOVqfjohbCdmnoYAL8ribfXfDZIguXMJ0Z5YXq5VogGUYifV/Uxt1RE6VL4LaZ4B8SHTKlAnYVZk6IbIgW7MhOsi+Tt858Fr9sKxchK/i0+0O9hgt8gnu0LadFVye3d3ydLp/vJ4wX0d1wCpmxOgtBE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Yuanhe Shu writes: > The !copy_mc fallbacks of copy_mc_user_highpage() and > copy_mc_highpage() return 0 after a plain copy. With PG_hwpoison > set while the data stays readable, there is no fault to recover > from: the copy completes, the destination folio carries no poison > marker, and the poison is consumed silently. IIUC, in all cases except debugging, reading poisoned memory will cause an MCE (x86), an SEA (arm), or similar. Otherwise, copy_mc on x86 would not work either. If so, we should only check is_page_hwpoison() before copying. > Check the source page with is_page_hwpoison() in both fallbacks, > before and after the copy, and return PAGE_SIZE, the > not-copied-bytes convention of the real copy_mc paths, so the > callers take their existing error paths. On archs with copy_mc > this code does not compile. > > Measured on arm64, where the fallback code compiles (10 rounds > each): COW copy throughput 1043.67 MB/s before and 1043.26 MB/s > after the patch, fork latency 348 vs 359 us, forced migration 57396 > vs 57654 MB/s - all within run-to-run noise. Could you implement a micro-benchmark in kernel to test your copy_mc functions? [snip] --- Best Regards, Huang, Ying