From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) (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 52D901519A9; Fri, 14 Feb 2025 06:54:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.191 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739516092; cv=none; b=cE8T2kz5gODwtm7jXkmoxCuE8rCbT7IgWqNKL18dkK8k+vrawX3sZrfoyJUkUgCbQVu45vkyPDAX2aM8FQzjiqYc8F7Lr6MapKzoLrNNLjP9JLfJW6SQ0OOZtX09Ht92JgFWAYZm7gkBf+YpbidgjX2eJ1lxMS5aQG+eYFdYlsc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739516092; c=relaxed/simple; bh=ObFBuaHdiUI3jKeFcePEaxXkVs0tu/Xgiv60cwCrCuM=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=dYJjjWM2pKtxQPtBrYakThRb0niQCstJjsIWZmVLFIAfxoMo/BRo0phZreRj5sBEpmVQnJb96bgLO7TS8LRbW9D0WPHVhjJXkT2+wjp/wPWjlU7L09vyUAVerDXVXrTs8bfKdd+Pv4+S6yI1CvP5CJHqExBxPzUmYScRVNbaqaU= 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=45.249.212.191 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 [172.19.163.17]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4YvN6n1XRQz1JK3d; Fri, 14 Feb 2025 14:53:21 +0800 (CST) Received: from kwepemd200019.china.huawei.com (unknown [7.221.188.193]) by mail.maildlp.com (Postfix) with ESMTPS id 475E31A0190; Fri, 14 Feb 2025 14:54:46 +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; Fri, 14 Feb 2025 14:54:45 +0800 Subject: Re: [PATCH v1 4/4] mm/hwpoison: Fix incorrect "not recovered" report for recovered clean pages To: Shuai Xue CC: , , , , , , , , , , , , , "nao.horiguchi@gmail.com" References: <20250211060200.33845-1-xueshuai@linux.alibaba.com> <20250211060200.33845-5-xueshuai@linux.alibaba.com> <5f116840-60df-c6d9-d7ff-dcf1dce7773f@huawei.com> <3820329d-20e3-49ee-a329-aac7393c6df3@linux.alibaba.com> <23251c74-cc50-012c-409f-c45117b52b16@huawei.com> <84ed4048-606e-47bf-98ad-d850cf30d60d@linux.alibaba.com> From: Miaohe Lin Message-ID: <9f54f518-2be4-7e44-0d6e-c03c53149b97@huawei.com> Date: Fri, 14 Feb 2025 14:54:44 +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: <84ed4048-606e-47bf-98ad-d850cf30d60d@linux.alibaba.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemd200019.china.huawei.com (7.221.188.193) On 2025/2/13 14:59, Shuai Xue wrote: > > > 在 2025/2/13 11:20, Miaohe Lin 写道: >> On 2025/2/12 21:55, Shuai Xue wrote: >>> >>> >>> 在 2025/2/12 16:09, Miaohe Lin 写道: >>>> On 2025/2/11 14:02, 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. >>>>> >>>>> 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. However, for clean pages, the >>>>> TTU_HWPOISON flag is cleared, leaving the PTE unchanged and not converted >>>>> to a hwpoison entry. Consequently, for an unmapped dirty page, the PTE is >>>>> marked as a hwpoison entry allowing kill_accessing_process() to: >>>>> >>>>> - call walk_page_range() and return 1 >>>>> - 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. >>>>> >>>>> 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 -EHWPOISON if no hwpoison PTE entry is found, preventing >>>>> an unnecessary SIGBUS. >>>> >>>> Thanks for your patch. >>>> >>>>> >>>>> Fixes: 046545a661af ("mm/hwpoison: fix error page recovered but reported "not recovered"") >>>>> Signed-off-by: Shuai Xue >>>>> --- >>>>>    mm/memory-failure.c | 5 ++--- >>>>>    1 file changed, 2 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>>>> index 995a15eb67e2..f9a6b136a6f0 100644 >>>>> --- a/mm/memory-failure.c >>>>> +++ b/mm/memory-failure.c >>>>> @@ -883,10 +883,9 @@ static int kill_accessing_process(struct task_struct *p, unsigned long pfn, >>>>>                      (void *)&priv); >>>>>        if (ret == 1 && priv.tk.addr) >>>>>            kill_proc(&priv.tk, pfn, flags); >>>>> -    else >>>>> -        ret = 0; >>>>>        mmap_read_unlock(p->mm); >>>>> -    return ret > 0 ? -EHWPOISON : -EFAULT; >>>>> + >>>>> +    return ret >= 0 ? -EHWPOISON : -EFAULT; >>>> >>>> IIUC, kill_accessing_process() is supposed to return -EHWPOISON to notify that SIGBUS is already >>>> sent to the process and kill_me_maybe() doesn't have to send it again. But with your change, >>>> kill_accessing_process() will return -EHWPOISON even if SIGBUS is not sent. Does this break >>>> the semantics of -EHWPOISON? >>> >>> Yes, from the comment of kill_me_maybe(), >>> >>>       * -EHWPOISON from memory_failure() means that it already sent SIGBUS >>>       * to the current process with the proper error info, >>>       * -EOPNOTSUPP means hwpoison_filter() filtered the error event, >>> >>> this patch break the comment. >>> >>> But the defination of EHWPOISON is quite different from the comment. >>> >>>   #define EHWPOISON    133    /* Memory page has hardware error */ >>> >>> As for this issue, returning 0 or EHWPOISON can both prevent a SIGBUS signal >>> from being sent in kill_me_maybe(). >>> >>> Which way do you prefer? >>> >>>> >>>> BTW I scanned the code of walk_page_range(). It seems with implementation of hwpoison_walk_ops >>>> walk_page_range() will only return 0 or 1, i.e. always >= 0. So kill_accessing_process() will always >>>> return -EHWPOISON if this patch is applied. >>>> >>>> Correct me if I miss something. >>> >>> Yes, you are right. Let's count the cases one by one: >>> >>> 1. clean page: try_to_remap(!TTU_HWPOISON), walk_page_range() will return 0 and >> >> Do you mean try_to_unmap? > > Yes, sorry for the typo. >> >>> we should not send sigbus in kill_me_maybe(). >>> >>> 2. dirty page: >>> 2.1 MCE wins race >>>            CMCI:w/o Action Require         MCE: w/ Action Require >>>                                        TestSetPageHWPoison >>>        TestSetPageHWPoison >>>        return -EHWPOISON >>>                                        try_to_unmap(TTU_HWPOISON) >>>                                        kill_proc in hwpoison_user_mappings() >>> >>> If MCE wins the race, because the flag of memory_fialure() called by CMCI is >>> not set as MF_ACTION_REQUIRED, everything goes well, kill_proc() will send >>> SIGBUS in hwpoison_user_mappings(). >>> >>> 2.2 CMCI win >>>            CMCI:w/o Action Require         MCE: w/ Action Require >>>      TestSetPageHWPoison >>>      try_to_unmap(TTU_HWPOISON) >>>                                         walk_page_range() return 1 due to hwpoison PTE entry >>>                                         kill_proc in kill_accessing_process() >>> >>> If the CMCI wins the race, we need to kill the process in >>> kill_accessing_process(). And if try_to_remap() success, everything goes well, >>> kill_proc() will send SIGBUS in kill_accessing_process(). >>> >>> But if try_to_remap() fails, the PTE entry will not be marked as hwpoison, and >>> walk_page_range() return 0 as case 1 clean page, NO SIGBUS will be sent. >> >> If try_to_unmap() fails, the PTE entry will still point to the dirty page. Then in >> check_hwpoisoned_entry(), we will have pfn == poisoned_pfn. So walk_page_range() >> will return 1 in this case. Or am I miss something? >> > > You’re right; I overlooked the pte_present() branch. > > Therefore, in the walk_page_range() function: > - It returns 0 when the poison page is a clean page. > - It returns 1 when CMCI wins, regardless of whether try_to_unmap succeeds >   or fails. > > Then the patch will be like: > > @@ -883,10 +883,9 @@ static int kill_accessing_process(struct task_struct *p, unsigned long pfn, >                    (void *)&priv); >      if (ret == 1 && priv.tk.addr) >          kill_proc(&priv.tk, pfn, flags); > -    else > -        ret = 0; >      mmap_read_unlock(p->mm); > -    return ret > 0 ? -EHWPOISON : -EFAULT; > + > +    return ret > 0 ? -EHWPOISON : 0; > > Here, returning 0 indicates that memory_failure() successfully handled the > error by dropping the clean page. I'm not sure whether there's another scene that can make walk_page_range() returns 0. But if the only reason for walk_page_range() returning 0 is the poison page is a clean page and it's dropped, then this modification should be appropriate. With this change, the callers never send SIGBUS now. They might need to be changed too. Thanks. . > > >>> >>> In summary, hwpoison_walk_ops cannot distinguish between try_to_unmap failing >>> and causing the PTE entry not to be set to hwpoison, and a clean page that >>> originally does not have the PTE entry set to hwpoison. >> >> Is it possible current process is not the one accessing the hwpoisoned page? E.g. memory_failure >> is deferred and called from kworker context or something like that. If it's possible, this is >> another scene needs to be considered. > > Yes, it possibale. > > But kill_accessing_process() will only be called with MF_ACTION_REQUIRED. > MF_ACTION_REQUIRED indates that current process is exactly the one accesing the > poison data. > > Fox x86 platform, GHES driver may queue a kwoker to defer memory_failure() with > flag=0.  So kill_accessing_process() will not be called in such case. > > Thanks. > Shuai > .