From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) (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 7B772204696; Thu, 13 Feb 2025 03:20:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739416812; cv=none; b=Z8gQTzuaKbc+QTxXyn9ysq889BiM1NhD71z3mXvufItXZl/fTpg9eOEAeatKzVwiQFcH3FBmKX35HLos9twzsVPBnNn8BQ9HgBvXPbvSXN0k/QUYsirqoh84cN4EapsJiNJ0EERIzGeubpmEJjD/k89q7ewbY9dk11yQtN9q2Go= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739416812; c=relaxed/simple; bh=W9Se1/UwvZd2QD0glU9KagGJZ9GfdMBk7hk4Mok2Dmw=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=P/uN8Rh2L3LQ2eEinb22NrNQqfjrfhk8CbxfS0DiMvon/DCOqdrXsvKHmD+tHMk2gWHbUrITVjOdwxANnSKWdfv3Yzt+IHsYiAW/nct+AzIWynAvoWtKG6CS8DIjGCn2jbkNji13ewDtzimwD6wwppXuSAu+QcwO77PAWlzranc= 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=45.249.212.187 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 szxga01-in.huawei.com (SkyGuard) with ESMTP id 4YtgM41krqzkXPf; Thu, 13 Feb 2025 11:16:32 +0800 (CST) Received: from kwepemd200019.china.huawei.com (unknown [7.221.188.193]) by mail.maildlp.com (Postfix) with ESMTPS id 8C2E31800DB; Thu, 13 Feb 2025 11:20:05 +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; Thu, 13 Feb 2025 11:20:04 +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> From: Miaohe Lin Message-ID: <23251c74-cc50-012c-409f-c45117b52b16@huawei.com> Date: Thu, 13 Feb 2025 11:20:03 +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: <3820329d-20e3-49ee-a329-aac7393c6df3@linux.alibaba.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemd200019.china.huawei.com (7.221.188.193) 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? > 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? > > 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. Thanks. .