From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05F6CC433F5 for ; Thu, 5 May 2022 13:42:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1378140AbiEENpj (ORCPT ); Thu, 5 May 2022 09:45:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57260 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235092AbiEENpg (ORCPT ); Thu, 5 May 2022 09:45:36 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1026F3B037 for ; Thu, 5 May 2022 06:41:56 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 659786144D for ; Thu, 5 May 2022 13:41:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7D69C385A8; Thu, 5 May 2022 13:41:51 +0000 (UTC) Date: Thu, 5 May 2022 14:41:48 +0100 From: Catalin Marinas To: Tong Tiangen Cc: Mark Rutland , James Morse , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Robin Murphy , Dave Hansen , Will Deacon , Alexander Viro , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , x86@kernel.org, "H . Peter Anvin" , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Kefeng Wang , Xie XiuQi , Guohanjun Subject: Re: [PATCH -next v4 4/7] arm64: add copy_{to, from}_user to machine check safe Message-ID: References: <20220420030418.3189040-1-tongtiangen@huawei.com> <20220420030418.3189040-5-tongtiangen@huawei.com> <7da54d72-e5fa-41b5-67ea-a0b084e4c94a@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7da54d72-e5fa-41b5-67ea-a0b084e4c94a@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 05, 2022 at 02:39:43PM +0800, Tong Tiangen wrote: > 在 2022/5/4 18:26, Catalin Marinas 写道: > > On Wed, Apr 20, 2022 at 03:04:15AM +0000, Tong Tiangen wrote: > > > Add copy_{to, from}_user() to machine check safe. > > > > > > If copy fail due to hardware memory error, only the relevant processes are > > > affected, so killing the user process and isolate the user page with > > > hardware memory errors is a more reasonable choice than kernel panic. > > > > Just to make sure I understand - we can only recover if the fault is in > > a user page. That is, for a copy_from_user(), we can only handle the > > faults in the source address, not the destination. > > At the beginning, I also thought we can only recover if the fault is in a > user page. > After discussion with a Mark[1], I think no matter user page or kernel page, > as long as it is triggered by the user process, only related processes will > be affected. According to this > understanding, it seems that all uaccess can be recovered. > > [1]https://patchwork.kernel.org/project/linux-arm-kernel/patch/20220406091311.3354723-6-tongtiangen@huawei.com/ We can indeed safely skip this copy and return an error just like pretending there was a user page fault. However, my point was more around the "isolate the user page with hardware memory errors". If the fault is on a kernel address, there's not much you can do about. You'll likely trigger it later when you try to access that address (maybe it was freed and re-allocated). Do we hope we won't get the same error again on that kernel address? -- Catalin