From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) (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 12703149E13 for ; Thu, 3 Apr 2025 02:48:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743648493; cv=none; b=Y38DqLwquHF3ii3ICMhQadbOcOxiDUAbgWtKdEWrttXH7Fm9TJ6tCFEtCWYTPcoPk+F213hRveAobzGWvEBJ4zFw+q1BCz0/QN4ZDnoqWi81I0Z+JBKEbkxaX9y64BD2eujmEgtS6dGqSsBbW88far3TCf/I2zMgBpHfIMjVOYQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743648493; c=relaxed/simple; bh=cKD/uq5gRClbepJa8muRX6JDWvbLXhWsZqu0fN23jlM=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=Cks1liplJ2S9JSdcV6HaPysWSt6yInxLkkCq4Gqwpy5hv1sz5vj2HLEvdJ10JacF/t42+dRZOROeB8ATw8Jo+uNJuXNdcXLXnp2SMBOpDkDpCbfIU+s7OvNv3xBd3qMrKchozlF0aiW0qNm+J5UG/DwpqmZNgwaOa/oHFNCkMM0= 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=45.249.212.189 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 szxga03-in.huawei.com (SkyGuard) with ESMTP id 4ZSmKq0chQzHrDQ; Thu, 3 Apr 2025 10:44:47 +0800 (CST) Received: from kwepemk500005.china.huawei.com (unknown [7.202.194.90]) by mail.maildlp.com (Postfix) with ESMTPS id B33E31800EB; Thu, 3 Apr 2025 10:48:07 +0800 (CST) Received: from [10.174.179.234] (10.174.179.234) by kwepemk500005.china.huawei.com (7.202.194.90) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Thu, 3 Apr 2025 10:48:05 +0800 Message-ID: <82bf1b64-d887-c50b-17b1-2de978896d44@huawei.com> Date: Thu, 3 Apr 2025 10:48:04 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v13 2/5] arm64: add support for ARCH_HAS_COPY_MC To: "Luck, Tony" CC: Catalin Marinas , Mark Rutland , Jonathan Cameron , Mauro Carvalho Chehab , Will Deacon , Andrew Morton , James Morse , Robin Murphy , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Michael Ellerman , Nicholas Piggin , Andrey Ryabinin , Alexander Potapenko , Christophe Leroy , Aneesh Kumar K.V , "Naveen N. Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "H. Peter Anvin" , Madhavan Srinivasan , , , , , , , Guohanjun References: <20241209024257.3618492-1-tongtiangen@huawei.com> <20241209024257.3618492-3-tongtiangen@huawei.com> From: Tong Tiangen In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemk500005.china.huawei.com (7.202.194.90) 在 2025/3/25 0:54, Luck, Tony 写道: > On Fri, Feb 14, 2025 at 09:44:02AM +0800, Tong Tiangen wrote: >> >> >> 在 2025/2/13 0:21, Catalin Marinas 写道: >>> (catching up with old threads) >>> >>> On Mon, Dec 09, 2024 at 10:42:54AM +0800, Tong Tiangen wrote: >>>> For the arm64 kernel, when it processes hardware memory errors for >>>> synchronize notifications(do_sea()), if the errors is consumed within the >>>> kernel, the current processing is panic. However, it is not optimal. >>>> >>>> Take copy_from/to_user for example, If ld* triggers a memory error, even in >>>> kernel mode, only the associated process is affected. Killing the user >>>> process and isolating the corrupt page is a better choice. >>> >>> I agree that killing the user process and isolating the page is a better >>> choice but I don't see how the latter happens after this patch. Which >>> page would be isolated? >> >> The SEA is triggered when the page with hardware error is read. After >> that, the page is isolated in memory_failure() (mf). The processing of >> mf is mentioned in the comments of do_sea(). >> >> /* >> * APEI claimed this as a firmware-first notification. >> * Some processing deferred to task_work before ret_to_user(). >> */ >> >> Some processing include mf. >> >>> >>>> Add new fixup type EX_TYPE_KACCESS_ERR_ZERO_MEM_ERR to identify insn >>>> that can recover from memory errors triggered by access to kernel memory, >>>> and this fixup type is used in __arch_copy_to_user(), This make the regular >>>> copy_to_user() will handle kernel memory errors. >>> >>> Is the assumption that the error on accessing kernel memory is >>> transient? There's no way to isolate the kernel page and also no point >>> in isolating the destination page either. >> >> Yes, it's transient, the kernel page in mf can't be isolated, the >> transient access (ld) of this kernel page is currently expected to kill >> the user-mode process to avoid error spread. >> >> >> The SEA processes synchronization errors. Only hardware errors on the >> source page can be detected (Through synchronous ld insn) and processed. >> The destination page cannot be processed. > > I've considered the copy_to_user() case as only partially fixable. There > are lots of cases to consider: > > 1) Many places where drivers copy to user in ioctl(2) calls. > Killing the application solves the immediate problem, but if > the problem with kernel memory is not transient, then you > may run into it again. > > 2) Copy from Linux page cache to user for a read(2) system call. > This one is a candidate for recovery. Might need help from the > file system code. If the kernel page is a clean copy of data in > the file system, then drop this page and re-read from storage > into a new page. Then resume the copy_to_user(). > If the page is modified, then need some file system action to > somehow mark this range of addresses in the file as lost forever. > First step in tackling this case is identifying that the source > address is a page cache page. > > 3) Probably many other places where the kernel copies to user for > other system calls. Would need to look at these on a case by case > basis. Likely most have the same issue as ioctl(2) above. 1) 3) Yes, in extreme cases, user-mode processes may be killed all the time. The hardware error that repeatedly triggered in the same page, in this case, firmware maybe report a fatal error, if yes, this problem can be solved. 2) This is indeed a workaround, somewhat complex, but it seems worthwhile to avoid kernel panic. Sorry for didn't catch your reply in time:) Thanks, Tong. > > -Tony > > .