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 CAED6C10F1B for ; Sat, 17 Dec 2022 02:59:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230106AbiLQC74 (ORCPT ); Fri, 16 Dec 2022 21:59:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56492 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230043AbiLQC7v (ORCPT ); Fri, 16 Dec 2022 21:59:51 -0500 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25F8F19C1F for ; Fri, 16 Dec 2022 18:59:48 -0800 (PST) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4NYrJj334wz16Lg7; Sat, 17 Dec 2022 10:58:45 +0800 (CST) Received: from [10.174.151.185] (10.174.151.185) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.34; Sat, 17 Dec 2022 10:59:46 +0800 Subject: Re: [PATCH 2/2] mm: Fix a few rare cases of using swapin error pte marker To: Peter Xu , , CC: Andrea Arcangeli , Pengfei Xu , Nadav Amit , David Hildenbrand , Andrew Morton , Huang Ying References: <20221214200453.1772655-1-peterx@redhat.com> <20221214200453.1772655-3-peterx@redhat.com> From: Miaohe Lin Message-ID: <9669705e-1bee-c789-86c7-6e3f6e28d109@huawei.com> Date: Sat, 17 Dec 2022 10:59:46 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20221214200453.1772655-3-peterx@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.151.185] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/12/15 4:04, Peter Xu wrote: > This patch should harden commit 15520a3f0469 ("mm: use pte markers for swap > errors") on using pte markers for swapin errors on a few corner cases. > > 1. Propagate swapin errors across fork()s: if there're swapin errors in > the parent mm, after fork()s the child should sigbus too when an error > page is accessed. > > 2. Fix a rare condition race in pte_marker_clear() where a uffd-wp pte > marker can be quickly switched to a swapin error. > > 3. Explicitly ignore swapin error pte markers in change_protection(). > > I mostly don't worry on (2) or (3) at all, but we should still have them. > Case (1) is special because it can potentially cause silent data corrupt on > child when parent has swapin error triggered with swapoff, but since swapin > error is rare itself already it's probably not easy to trigger either. > > Currently there is a priority difference between the uffd-wp bit and the > swapin error entry, in which the swapin error always has higher > priority (e.g. we don't need to wr-protect a swapin error pte marker). > > If there will be a 3rd bit introduced, we'll probably need to consider a > more involved approach so we may need to start operate on the bits. Let's > leave that for later. > > This patch is tested with case (1) explicitly where we'll get corrupted > data before in the child if there's existing swapin error pte markers, and > after patch applied the child can be rightfully killed. > > We don't need to copy stable for this one since 15520a3f0469 just landed as > part of v6.2-rc1, only "Fixes" applied. > > Fixes: 15520a3f0469 ("mm: use pte markers for swap errors") > Signed-off-by: Peter Xu Looks good to me. Thanks. Reviewed-by: Miaohe Lin Thanks, Miaohe Lin