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Mon, 29 Sep 2025 20:29:43 +0800 (CST) Received: from dggemv705-chm.china.huawei.com (unknown [10.3.19.32]) by mail.maildlp.com (Postfix) with ESMTPS id AD39C180042; Mon, 29 Sep 2025 20:29:53 +0800 (CST) Received: from kwepemq500010.china.huawei.com (7.202.194.235) by dggemv705-chm.china.huawei.com (10.3.19.32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 29 Sep 2025 20:29:53 +0800 Received: from [10.173.125.236] (10.173.125.236) by kwepemq500010.china.huawei.com (7.202.194.235) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 29 Sep 2025 20:29:52 +0800 Subject: Re: [PATCH 1/1] mm: prevent poison consumption when splitting THP To: Jiaqi Yan , Qiuxu Zhuo CC: , , , , , , , , , , , , , , , Andrew Zaborowski References: <20250928032842.1399147-1-qiuxu.zhuo@intel.com> From: Miaohe Lin Message-ID: <5f117b73-8d7b-b233-a0a8-2a29ea6312a8@huawei.com> Date: Mon, 29 Sep 2025 20:29:42 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.125.236] X-ClientProxiedBy: kwepems200002.china.huawei.com (7.221.188.68) To kwepemq500010.china.huawei.com (7.202.194.235) X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5560B1C0009 X-Stat-Signature: 9ubtdwoxky9g6ub9nf1wkdj5gapkn8bj X-Rspam-User: X-HE-Tag: 1759148998-71239 X-HE-Meta: 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 Z67Fe6br wypHerHNeFiUXzeFZHdZxYqqNCQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/9/29 5:55, Jiaqi Yan wrote: > On Sat, Sep 27, 2025 at 8:30 PM Qiuxu Zhuo wrote: >> >> From: Andrew Zaborowski >> >> When performing memory error injection on a THP (Transparent Huge Page) >> mapped to userspace on an x86 server, the kernel panics with the following >> trace. The expected behavior is to terminate the affected process instead >> of panicking the kernel, as the x86 Machine Check code can recover from an >> in-userspace #MC. >> >> mce: [Hardware Error]: CPU 0: Machine Check Exception: f Bank 3: bd80000000070134 >> mce: [Hardware Error]: RIP 10: {memchr_inv+0x4c/0xf0} >> mce: [Hardware Error]: TSC afff7bbff88a ADDR 1d301b000 MISC 80 PPIN 1e741e77539027db >> mce: [Hardware Error]: PROCESSOR 0:d06d0 TIME 1758093249 SOCKET 0 APIC 0 microcode 80000320 >> mce: [Hardware Error]: Run the above through 'mcelog --ascii' >> mce: [Hardware Error]: Machine check: Data load in unrecoverable area of kernel >> Kernel panic - not syncing: Fatal local machine check >> >> The root cause of this panic is that handling a memory failure triggered by >> an in-userspace #MC necessitates splitting the THP. The splitting process >> employs a mechanism, implemented in try_to_map_unused_to_zeropage(), which >> reads the sub-pages of the THP to identify zero-filled pages. However, >> reading the sub-pages results in a second in-kernel #MC, occurring before >> the initial memory_failure() completes, ultimately leading to a kernel >> panic. See the kernel panic call trace on the two #MCs. >> >> First Machine Check occurs // [1] >> memory_failure() // [2] >> try_to_split_thp_page() >> split_huge_page() >> split_huge_page_to_list_to_order() >> __folio_split() // [3] >> remap_page() >> remove_migration_ptes() >> remove_migration_pte() >> try_to_map_unused_to_zeropage() > > Just an observation: Unfortunately THP only has PageHasHWPoisoned and > don't know the exact HWPoisoned page. Otherwise, we may still use > zeropage for these not HWPoisoned. IIUC, the raw error page will have HWPoisoned flag set while the THP has PageHasHWPoisoned set. So I think we could use zeropage for healthy sub-pages. Thanks. .