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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA37EC4332F for ; Fri, 16 Dec 2022 09:04:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4C06A8E0003; Fri, 16 Dec 2022 04:04:36 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 479B58E0002; Fri, 16 Dec 2022 04:04:36 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 311788E0003; Fri, 16 Dec 2022 04:04:36 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 20E588E0002 for ; Fri, 16 Dec 2022 04:04:36 -0500 (EST) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id DD0BB1C5F3B for ; Fri, 16 Dec 2022 09:04:35 +0000 (UTC) X-FDA: 80247583710.05.D18649D Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf13.hostedemail.com (Postfix) with ESMTP id 3D92A20016 for ; Fri, 16 Dec 2022 09:04:32 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aozE8vGo; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1671181472; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=LJMVmx5617wnYVO/Ti21QHTcgxd/PcheSNh2Us8/9os=; b=WoszMXFGkqqvEbJDHd8skrHYnNcPauy78+SOvuPT2Pah74XSQbreMhKa9klbWbYM0Jculx NdwMrH/uyRoEab5rFv5BcuWLDfA9BE9DamatwC7qoM/jXi/e65L4VN+rJFOdNGrixpF4jB NqSac3u8dzAJiFAdJ/YR95706J44zEo= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aozE8vGo; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1671181472; a=rsa-sha256; cv=none; b=RDoCAOtXJIuZ7yvWlx91t4N3uI6gFZOec2LX+AIIAhY25+mymbes0BgUrNEkkLNMWJyWiy lNXZs8Xvrp7O5GvFG+lX/Dxrgguenrwh0tAhC+joKPuqER//uQqJVMQynQkm2G1yxozD0s HYbM8aA3KQzgz1pe2EhJuUXc5ZP1DA0= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671181471; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LJMVmx5617wnYVO/Ti21QHTcgxd/PcheSNh2Us8/9os=; b=aozE8vGo+gT+EvRZ0u9JZaPAUTu72QqzSOO5gkndp7sHZLKKpKpWn2sVaKP+GbXfdR81zB zydYcUitc0gjQVtlc0vKd13R4PZAfZ8bGVyxfqSEUxu5sA1rpvqIAZBA8JKfrx2q6ZC9OH FnFaK6lNS8atNHvVoPRzgkAgvw7qwBs= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-487-6fUvT_wQPa61cjLz1go7eQ-1; Fri, 16 Dec 2022 04:04:30 -0500 X-MC-Unique: 6fUvT_wQPa61cjLz1go7eQ-1 Received: by mail-wm1-f69.google.com with SMTP id a6-20020a05600c224600b003d1f3ed49adso421222wmm.4 for ; Fri, 16 Dec 2022 01:04:30 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:subject:organization:from :references:cc:to:content-language:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=LJMVmx5617wnYVO/Ti21QHTcgxd/PcheSNh2Us8/9os=; b=dqnJnK8MTwzeM6KJK3gYmb2IXh9Gi801+9PUTxONhobBT2Iew+fzSW/DGy3qaHBAGl 8QTP4dvdPUoMK3Qi4Cco0mL8DfblcQPIA5JoxiN1rQXPRAMOzKAqmUnTsjkw9XrnqyV/ kKr3Ml6DZdnO8HgATxEhKWBFMp/963orgQi0dYTcMcr+X4R8ZuAhF3CCjehfpgniDmtQ 8K1Yli5hZkK/q203Gkf9RsRTM7fe7MSK632twEwj4jvCkUTmkuUR0wsL7GqYxpbcDRzI sUCsLmqV4yoQAt4UcwaxbuVXVMxFqszw4c67eo+PcB3NQIHhMGpnm5LlrrUH/S34KYs/ MGfw== X-Gm-Message-State: ANoB5plPgfVVhhVRq66i76VqEwHb9zKVlkSU2UO1v0Npe4Kn91K86KB7 +2l52sJW0rVkpebb/Lh5biCUHP1/jUPIWndm0zzRMzSHGLLhjUqXN0/s8UppXahenM0uLOyZXli 9EFopw1t8eBE= X-Received: by 2002:a05:600c:5570:b0:3d1:ee6c:f897 with SMTP id ja16-20020a05600c557000b003d1ee6cf897mr24618890wmb.3.1671181469142; Fri, 16 Dec 2022 01:04:29 -0800 (PST) X-Google-Smtp-Source: AA0mqf44EaOB06LEJ5Xrw6HHHrPTv1tXz6Tk6ti4LOhrQzaZKR+fbWWGTZDSKlTS7qMorzGnBsu8Nw== X-Received: by 2002:a05:600c:5570:b0:3d1:ee6c:f897 with SMTP id ja16-20020a05600c557000b003d1ee6cf897mr24618865wmb.3.1671181468820; Fri, 16 Dec 2022 01:04:28 -0800 (PST) Received: from ?IPV6:2003:cb:c71c:3900:7211:d436:8d8b:531c? (p200300cbc71c39007211d4368d8b531c.dip0.t-ipconnect.de. [2003:cb:c71c:3900:7211:d436:8d8b:531c]) by smtp.gmail.com with ESMTPSA id k5-20020a05600c1c8500b003d237d60318sm2096196wms.2.2022.12.16.01.04.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 16 Dec 2022 01:04:28 -0800 (PST) Message-ID: <618b69be-0e99-e35f-04b3-9c63d78ece50@redhat.com> Date: Fri, 16 Dec 2022 10:04:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Andrea Arcangeli , Pengfei Xu , Nadav Amit , Andrew Morton , Miaohe Lin , Huang Ying , stable@vger.kernel.org References: <20221214200453.1772655-1-peterx@redhat.com> <20221214200453.1772655-2-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH 1/2] mm/uffd: Fix pte marker when fork() without fork event In-Reply-To: <20221214200453.1772655-2-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: nwf8k6emskdd8gyqryfzmczu44mmuwyg X-Rspam-User: X-Rspamd-Queue-Id: 3D92A20016 X-Rspamd-Server: rspam06 X-HE-Tag: 1671181472-995899 X-HE-Meta: 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 6gm32dnb 0l+ghAUgLTeEO8/e+d572l79BpW4J1gcbKeHqJkdPl/N4xN3Nyi9nT1N++iLD/k2ToBA6AKdU6mNdgoy88Siq/O8fldAwhXydbYQjGM0qyPrZN2Kmbsilc1ybJmfTxwtQG7auAomWVdF/8uVpvT/QUazZTcoHj+KwsaJNE/dPXU4km/7uaiDT+slsgi9k370bALYJCn4l+GDM5pRZ/7Ovq16EAA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 14.12.22 21:04, Peter Xu wrote: > When fork(), dst_vma is not guaranteed to have VM_UFFD_WP even if src may > have it and has pte marker installed. The warning is improper along with > the comment. The right thing is to inherit the pte marker when needed, or > keep the dst pte empty. > > A vague guess is this happened by an accident when there's the prior patch > to introduce src/dst vma into this helper during the uffd-wp feature got > developed and I probably messed up in the rebase, since if we replace > dst_vma with src_vma the warning & comment it all makes sense too. > > Hugetlb did exactly the right here (copy_hugetlb_page_range()). Fix the > general path. > > Reproducer: > > https://github.com/xupengfe/syzkaller_logs/blob/main/221208_115556_copy_page_range/repro.c > > Cc: # 5.19+ > Fixes: c56d1b62cce8 ("mm/shmem: handle uffd-wp during fork()") > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216808 > Reported-by: Pengfei Xu > Signed-off-by: Peter Xu > --- > mm/memory.c | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index aad226daf41b..032ef700c3e8 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -828,12 +828,8 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, > return -EBUSY; > return -ENOENT; > } else if (is_pte_marker_entry(entry)) { > - /* > - * We're copying the pgtable should only because dst_vma has > - * uffd-wp enabled, do sanity check. > - */ > - WARN_ON_ONCE(!userfaultfd_wp(dst_vma)); > - set_pte_at(dst_mm, addr, dst_pte, pte); > + if (userfaultfd_wp(dst_vma)) > + set_pte_at(dst_mm, addr, dst_pte, pte); > return 0; > } > if (!userfaultfd_wp(dst_vma)) Staring at the code first made me go "what about other PTE markers". I then looked into the discussion in patch #2. The fix as is is suboptimal, because it 1) Removes the warning which is good, but 2) Silently drops swapin errors now So it silently breaks something else temporarily ... I remember, that theoretically we could have multiple markers stored in a single PTE marker. Wouldn't it be cleaner to be able to "clean" specific markers from a PTE marker without having to special case on each and everyone? I mean, only uffd-wp is really special such that it might disappear for the target. Something like (pseudocode): if (!userfaultfd_wp(dst_vma)) pte_marker_clear_uff_wp(entry); if (!pte_marker_empty(entry)) { pte = make_pte_marker(pte_marker_get(entry)); set_pte_at(dst_mm, addr, dst_pte, pte); } Then this fix would be correct and backport-able even without #2. And it would work for new types of markers :) I'd prefer a fix that doesn't break something else temporarily, even if the stable backport might require 5 additional minutes to do. So squashing #2 into #1 would also work. -- Thanks, David / dhildenb