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 C1A88C282EC for ; Mon, 10 Mar 2025 18:50:45 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AE237280005; Mon, 10 Mar 2025 14:50:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A928E280004; Mon, 10 Mar 2025 14:50:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 93374280005; Mon, 10 Mar 2025 14:50:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 75BBB280004 for ; Mon, 10 Mar 2025 14:50:44 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 8152C813F5 for ; Mon, 10 Mar 2025 18:50:44 +0000 (UTC) X-FDA: 83206532808.01.0337F54 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf28.hostedemail.com (Postfix) with ESMTP id D2B3BC0009 for ; Mon, 10 Mar 2025 18:50:41 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ajnbanmd; spf=pass (imf28.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@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=1741632642; 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=wbs7NSbL6vKlRMHSJIXxZs2mfOWdL12EXaa0cm8bbjU=; b=d5IdEyPKuxnLz4Jlv0SdeT+m0NyElgFZVXqQEGKds2jQrjo4wxvCKugPgi6Q48hglQQ+Yq HobEkDouIMzs2RDA+hEEVwgzl+/KT5ytg/OO8Zg1e+ncSoQZ7+/OPcdwh2xZpIeMnH+Kqj LRxmJDg3YpdkeatsnY+oWpfn4CRgS6c= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ajnbanmd; spf=pass (imf28.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1741632642; a=rsa-sha256; cv=none; b=73bpqa21niOQmxR38QvGQZjeFI0mL1UVmcJhAg7aTzsmk8MZ00N1vV5jC6LJzCRmCK0TGT Fd6dPNL5Tpjta46vQhT4VPxCb/MJWonT6o4j8RtuEujUimd5ohHxKqxHmwexQlubE7Eu0z zhH4xRUahaNSCrDaI563mOfCSnuoPlc= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741632641; 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=wbs7NSbL6vKlRMHSJIXxZs2mfOWdL12EXaa0cm8bbjU=; b=ajnbanmdPykX022L/z2cJGliwZPyvVh4m4NdOiQsls5M83g/GM/e58J4Sss8ubfHDrz2cp JmbIAeZ4TNjdIKJZSzawiMBe93KCtLhqZcHIkjBAkGxZuPqOtm4ruA6QijNNBX3/4QtPDt jv7jVNJALY8ZLJN+NTIBY9+NSm9ARd0= Received: from mail-qv1-f70.google.com (mail-qv1-f70.google.com [209.85.219.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-511-5kob285BNYe_GAmaoSSYuA-1; Mon, 10 Mar 2025 14:50:39 -0400 X-MC-Unique: 5kob285BNYe_GAmaoSSYuA-1 X-Mimecast-MFC-AGG-ID: 5kob285BNYe_GAmaoSSYuA_1741632639 Received: by mail-qv1-f70.google.com with SMTP id 6a1803df08f44-6e8f9057432so9072396d6.1 for ; Mon, 10 Mar 2025 11:50:39 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741632638; x=1742237438; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=wbs7NSbL6vKlRMHSJIXxZs2mfOWdL12EXaa0cm8bbjU=; b=iRUaVG+ZN+xZp/p/IZJ4I8VI2+42a4n8wrD8vtgrRZNN/Oga4vnSpRPDFTTJRnVjf/ LEY7zoFpqVpeiCAVGH7VDEEFMu72t6m45zWb9KUF/KbModu/+jKRiY+FedjnKpGvO/MM I/hcGwECpsWAkuTL2c/aFb6Drnm0gsRlmon1o6F4aXG5XA54dDaJJLNIp1GVTg+AQ9gI CyaB7miNMMK0q70BTnEOWlKP4oKjqilFK4NTF9fQ/+Ea/T0ULlB68SJ+3nM/jaY0XBWr yySE5KuGeZWT7N/QJn9FWrOkwzxURLXeyvalzU5aDMeoNUXuxfqXN79JS/PLpPgyoB9I 3F4g== X-Forwarded-Encrypted: i=1; AJvYcCVmdH1Dx1eCYWAoY6yYiTpye6h3RfOEduWVAjaxPGFFjwTdsiD4humF6HNDPb9NeD1/qfKfpBfUjw==@kvack.org X-Gm-Message-State: AOJu0YweMD15y5EMczYJxGVj5+H84rqgoITgWdmCnIA2LvHq3XANCZxX CPHIYjkB5Kgwdj0tfbwm7ZRTm16Kbd5NqZQlhZHzzY3Drw6rHROABQro4yNraiF6KaEGBKKjv4f 5PH22DM5sa1gjQOmpADXcAMN9seNlX/zgmogQWPEg932sek2WA+zS1yCe X-Gm-Gg: ASbGncsGVb4EejNZTLDF8107Td3FgH8nlM2N7ug2mRveUi1BcCnDcgdgwJ8lnwjRCiu f2p62Ys5X+1bOjZPqfvgd8q1lfYEBFleP6ym8JHqk2tWLwU8l7xvDdbPs2ytQ3YyPEBVi8j//vU j6N2iu6VLirw7znWjgpgqtNBPmXlDr6uvf5GMRJ6hhacwDqO7MYq8NGxbomKxaffPKkiddAWz4k 7biP0fzK2tRj9t/Yg4IbwGHAsWXfcwAS3qgkcyQ/fCf31MgmfGwWdtGYM/RyVzJ7yrhQg3fjAPZ L/iOAzk= X-Received: by 2002:a05:6214:21cb:b0:6e8:9fcb:5f7d with SMTP id 6a1803df08f44-6e9006913cdmr229708416d6.36.1741632638611; Mon, 10 Mar 2025 11:50:38 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFie+mzm2Bw8VvHKP/u+MGW8Iw61YPMj501OCpii1PEfvhFOD2xnDZkzVVnlM30dQ3KOy/+cA== X-Received: by 2002:a05:6214:21cb:b0:6e8:9fcb:5f7d with SMTP id 6a1803df08f44-6e9006913cdmr229708106d6.36.1741632638222; Mon, 10 Mar 2025 11:50:38 -0700 (PDT) Received: from x1.local ([85.131.185.92]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6e8f7170958sm61093186d6.108.2025.03.10.11.50.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Mar 2025 11:50:37 -0700 (PDT) Date: Mon, 10 Mar 2025 14:50:34 -0400 From: Peter Xu To: Jinjiang Tu Cc: jimsiak , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-mm@kvack.org, wangkefeng.wang@huawei.com Subject: Re: Using userfaultfd with KVM's async page fault handling causes processes to hung waiting for mmap_lock to be released Message-ID: References: <79375b71-db2e-3e66-346b-254c90d915e2@cslab.ece.ntua.gr> <20250307072133.3522652-1-tujinjiang@huawei.com> <46ac83f7-d3e0-b667-7352-d853938c9fc9@huawei.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CCShLCEGEI9scctyAXcS1aySfMkdTUz2gq_cZNZJFy8_1741632639 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: D2B3BC0009 X-Stat-Signature: wyc516otyi75x7j1683fyqkbdhr4o6oj X-Rspamd-Server: rspam09 X-HE-Tag: 1741632641-566673 X-HE-Meta: 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 xcIgULci wOtKPVlMPnnIONoiVNxo3oDe2dORUhqV3uZRKq6Gy/vk9/EMC/OaMJnzGGN9RaEH7ytWoTosBC3z2thL3u9NGmh92pz4JWWuDq7XSpl9Yd/p6BIOo7OK6TgZp+rvu1/MEthHqEH/ggqjHZpBCLVoq8TGRWByyVVE7wryXAPjNfTnjI7BRjXXzDVM+3i1mvD3zHbIn1bm5e4tjidhC6kJ+hGc9qCMPXcUiewKh8Q+cDlmmdo77LvS5wx6Qzs3/1zqfBsvJLmOJgY3eISycFzQunmA3ZsvmdMIkuSzRf8vBmzShe7fiAnZuUPENCTj8O+uEOyaUtofO4v1/i6xqVEsEVV0atzTz9VUk+j8LYjKMUctHdjSi6B6hGsBncU61jZIY1Bm3Ze7xlIQdZ8RSdMQBBBMr6XWyMgtb7x3+NP9ZljmF3DwUnIc/Wd3EU41bkAJY6isMKps7zIvvCZj1pw+BSVZbAcWHY/+DDfEtXK+efSWvH7zCxT0xA293YiuQCULocyGE X-Bogosity: Ham, tests=bogofilter, spamicity=0.000028, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 10, 2025 at 02:40:35PM +0800, Jinjiang Tu wrote: > > 在 2025/3/8 6:41, Peter Xu 写道: > > On Fri, Mar 07, 2025 at 03:11:09PM +0200, jimsiak wrote: > > > Hi, > > > > > > From my side, I managed to avoid the freezing of processes with the > > > following change in function userfaultfd_release() in file fs/userfaultfd.c > > > (https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L842): > > > > > > I moved the following command from line 851: > > > WRITE_ONCE(ctx->released, true); > > > (https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L851) > > > > > > to line 905, that is exactly before the functions returns 0. > > > > > > That simple workaround worked for my use case but I am far from sure that is > > > a correct/sufficient fix for the problem at hand. > > Updating the field after userfaultfd_ctx_put() might mean UAF, afaict. > > > > Maybe it's possible to remove ctx->released but only rely on the mmap write > > lock. However that'll need some closer look and more thoughts. > > > > To me, the more straightforward way to fix it is to use the patch I > > mentioned in the other email: > > > > https://lore.kernel.org/all/ZLmT3BfcmltfFvbq@x1n/ > > > > Or does it mean it didn't work at all? > > This patch works for me. mlock() syscall calls GUP with FOLL_UNLOCKABLE and > allows to release mmap lock and retry. > > But other GUP call without FOLL_UNLOCKABLE will return VM_FAULT_SIGBUS, > is it a regression for the below commit？ Do you have an explicit reproducer / use case of such? AFAIU, below commit should only change it from SIGBUS to NOPAGE when "released" is set. I don't see how it can regress on !FOLL_UNLOCKABLE. Thanks, > > commit 656710a60e3693911bee3a355d2f2bbae3faba33 > Author: Andrea Arcangeli > Date: Fri Sep 8 16:12:42 2017 -0700 > > userfaultfd: non-cooperative: closing the uffd without triggering SIGBUS > > > > > Thanks, > > > -- Peter Xu