From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AB9DB2C182; Wed, 12 Mar 2025 06:39:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741761559; cv=none; b=Jiq0qSju0JmbXKm6LVSlEwNTkEJnDA9ofhEytmCBtxOPK7x0lpD1GFg+oI6CNennnt0ECM5p7HQk6Z2ZXy7o0mI5vkI+3Lj8to/5LpWnL6X6izMxVmy/2hqtJi9uPgfuOqUt1CHCLCpchL8t4SvlRLlTSI6rEUOK2oAlq0RiMFM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741761559; c=relaxed/simple; bh=x+qKEywmekSRK3kHMQCREugxjGBlHkojqfQG4iSOqZU=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=ECe+kDEwtr6za70TcewREScTJ7RYv2ZgTNQMSOdYXN2Pui2nSsD3AbOxQHlc5l95urWXqr8i5ig1Wn5r3a/Pi2LCPxTeFQ8lmBJRFAHA3Z5sse1Gd1jK9sAcHm02KwS5NjT1uo7apQGlAa1lBf0ved9KL98r1nIl+AmwwTAY5nw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.252]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4ZCLVN3j4HzCs97; Wed, 12 Mar 2025 14:35:40 +0800 (CST) Received: from kwepemd200019.china.huawei.com (unknown [7.221.188.193]) by mail.maildlp.com (Postfix) with ESMTPS id 42B661800CD; Wed, 12 Mar 2025 14:39:13 +0800 (CST) Received: from [10.173.127.72] (10.173.127.72) by kwepemd200019.china.huawei.com (7.221.188.193) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Wed, 12 Mar 2025 14:39:11 +0800 Subject: Re: [PATCH v4 2/3] mm/hwpoison: Do not send SIGBUS to processes with recovered clean pages To: Shuai Xue CC: , , , , , , , , , , , , , , , , , References: <20250307054404.73877-1-xueshuai@linux.alibaba.com> <20250307054404.73877-3-xueshuai@linux.alibaba.com> From: Miaohe Lin Message-ID: <662a16ee-66d3-3fc8-6488-8788bcfbe84e@huawei.com> Date: Wed, 12 Mar 2025 14:39:10 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20250307054404.73877-3-xueshuai@linux.alibaba.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemd200019.china.huawei.com (7.221.188.193) On 2025/3/7 13:44, Shuai Xue wrote: > When an uncorrected memory error is consumed there is a race between the > CMCI from the memory controller reporting an uncorrected error with a UCNA > signature, and the core reporting and SRAR signature machine check when the > data is about to be consumed. > > - Background: why *UN*corrected errors tied to *C*MCI in Intel platform [1] > > Prior to Icelake memory controllers reported patrol scrub events that > detected a previously unseen uncorrected error in memory by signaling a > broadcast machine check with an SRAO (Software Recoverable Action Optional) > signature in the machine check bank. This was overkill because it's not an > urgent problem that no core is on the verge of consuming that bad data. > It's also found that multi SRAO UCE may cause nested MCE interrupts and > finally become an IERR. > > Hence, Intel downgrades the machine check bank signature of patrol > scrub from SRAO to UCNA (Uncorrected, No Action required), and signal > changed to #CMCI. Just to add to the confusion, Linux does take an action > (in uc_decode_notifier()) to try to offline the page despite the UC*NA* > signature name. > > - Background: why #CMCI and #MCE race when poison is consuming in Intel platform [1] > > Having decided that CMCI/UCNA is the best action for patrol scrub errors, > the memory controller uses it for reads too. But the memory controller is > executing asynchronously from the core, and can't tell the difference > between a "real" read and a speculative read. So it will do CMCI/UCNA if an > error is found in any read. > > Thus: > > 1) Core is clever and thinks address A is needed soon, issues a speculative read. > 2) Core finds it is going to use address A soon after sending the read request > 3) The CMCI from the memory controller is in a race with MCE from the core > that will soon try to retire the load from address A. > > Quite often (because speculation has got better) the CMCI from the memory > controller is delivered before the core is committed to the instruction > reading address A, so the interrupt is taken, and Linux offlines the page > (marking it as poison). > > - Why user process is killed for instr case > > Commit 046545a661af ("mm/hwpoison: fix error page recovered but reported > "not recovered"") tries to fix noise message "Memory error not recovered" > and skips duplicate SIGBUSs due to the race. But it also introduced a bug > that kill_accessing_process() return -EHWPOISON for instr case, as result, > kill_me_maybe() send a SIGBUS to user process. > > If the CMCI wins that race, the page is marked poisoned when > uc_decode_notifier() calls memory_failure(). For dirty pages, > memory_failure() invokes try_to_unmap() with the TTU_HWPOISON flag, > converting the PTE to a hwpoison entry. As a result, > kill_accessing_process(): > > - call walk_page_range() and return 1 regardless of whether > try_to_unmap() succeeds or fails, > - call kill_proc() to make sure a SIGBUS is sent > - return -EHWPOISON to indicate that SIGBUS is already sent to the > process and kill_me_maybe() doesn't have to send it again. > > However, for clean pages, the TTU_HWPOISON flag is cleared, leaving the > PTE unchanged and not converted to a hwpoison entry. Conversely, for > clean pages where PTE entries are not marked as hwpoison, > kill_accessing_process() returns -EFAULT, causing kill_me_maybe() to > send a SIGBUS. > > Console log looks like this: > > Memory failure: 0x827ca68: corrupted page was clean: dropped without side effects > Memory failure: 0x827ca68: recovery action for clean LRU page: Recovered > Memory failure: 0x827ca68: already hardware poisoned > mce: Memory error not recovered > > To fix it, return 0 for "corrupted page was clean", preventing an > unnecessary SIGBUS to user process. > > [1] https://lore.kernel.org/lkml/20250217063335.22257-1-xueshuai@linux.alibaba.com/T/#mba94f1305b3009dd340ce4114d3221fe810d1871 > Fixes: 046545a661af ("mm/hwpoison: fix error page recovered but reported "not recovered"") > Signed-off-by: Shuai Xue > Cc: stable@vger.kernel.org Thanks for your detailed commit log. This patch looks good to me. Acked-by: Miaohe Lin Thanks. .