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 8752EC7618E for ; Mon, 24 Apr 2023 10:18:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E929B6B0071; Mon, 24 Apr 2023 06:18:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E42E96B0074; Mon, 24 Apr 2023 06:18:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CE3676B0075; Mon, 24 Apr 2023 06:18:00 -0400 (EDT) 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 BBC466B0071 for ; Mon, 24 Apr 2023 06:18:00 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 7CBE28025D for ; Mon, 24 Apr 2023 10:18:00 +0000 (UTC) X-FDA: 80715883920.27.86A3995 Received: from mail-wm1-f50.google.com (mail-wm1-f50.google.com [209.85.128.50]) by imf30.hostedemail.com (Postfix) with ESMTP id 9332D8000C for ; Mon, 24 Apr 2023 10:17:58 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=gmail.com header.s=20221208 header.b=TqsT5bDL; spf=pass (imf30.hostedemail.com: domain of lstoakes@gmail.com designates 209.85.128.50 as permitted sender) smtp.mailfrom=lstoakes@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1682331478; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=sFd3GouLvmJwZXxGkUryj0wCtEPdyUrIZGRi3VcHFcY=; b=NjxtI1rmDGWd16HESCHZXZK+hnbIKnW6xrr8M0lHkfleIDXDpkN0ay08t1kGQnGXepw9Hd krNOKOg22OAeiOmjFF/ScCdcc8NyWttPprEs2XPxBXZk0wzlXdxegJW9TWfIPkaVEfpDgo FiobSpcmp2d67lKyGuNuorx+VS4CRxs= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=gmail.com header.s=20221208 header.b=TqsT5bDL; spf=pass (imf30.hostedemail.com: domain of lstoakes@gmail.com designates 209.85.128.50 as permitted sender) smtp.mailfrom=lstoakes@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1682331478; a=rsa-sha256; cv=none; b=6+V/Y2dnW5RIA/0h3Yvyc2yVDT/aSSdUw0SW4PrKnhS4tCM8crNJa4bGz/Ujtk6PZd41FR PJr72XP9OltiuNUNM42428uKYEGVPyjeUnl1wdPHwnEvXqFFX1g5nJgBWZVK9VPnCoS2lU Vh34CmJgMRHFR9TjAul4ihAozDWGq68= Received: by mail-wm1-f50.google.com with SMTP id 5b1f17b1804b1-3f195b164c4so16937095e9.1 for ; Mon, 24 Apr 2023 03:17:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1682331477; x=1684923477; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=sFd3GouLvmJwZXxGkUryj0wCtEPdyUrIZGRi3VcHFcY=; b=TqsT5bDLQhdBasdYkLmm+ue2xSgsEVBAjc5YTj++1vp6A3jb/eAm2ISqbClYNA/bN3 Bm0Qobi1sk/79zsr5IujFFPFlbsGzbAi1EJzMSmku+dNUifDgkAbCbcM8YUtWcBVvZOy SVPpWE5OWQfTe1GQr8ZTxOp6tt3VCUbd2OuOAC/DfDigTp0Uj1Rx+xCoGvzmour5y5R+ 4Hu3Tw5p+fFJfRaY5cfLbeLqTcGzpFGk6nHgmtiTQqRoAbl4T73JR4lVcu+fut660/g4 rcTw4Qo24E64xvf+zM2d8K0I3IEMc/kusIdXVd5+7w3YBNQEVSY8dQymZOSt9O+uppQ5 sLHw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1682331477; x=1684923477; h=in-reply-to: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=sFd3GouLvmJwZXxGkUryj0wCtEPdyUrIZGRi3VcHFcY=; b=R9PbxjxjqZmCFllPsbC+pFpVD7oPycEN/wFilZU44DnzkSoViXhMYJqgvJbPKRkabN Z+zEbJmiFbKyescM0Q+cwFFTFV/x0Wf2bRRcnYorJfF6DsJM1sU8Q5qxw7Gs7l6gs7mZ A7cNT9m71+BZziMnZ3JJ7V4Ujjo130+8fJT0r3PQc6FZFh/rzFWsSKBSK8UTBvMNyyq7 kNJsjdFKeW66kjYb6BiJv2sQAlstlQztHrFpoWhJSmW8RmZhlgDRD36BZvygjAy1uXZH rY+fo18jKDPlP0Qn2IsnHpcDKUp+fnY3WXEH7gcqpIg2lqmL+8Ho4jvn26gJjDt83UCu DqwA== X-Gm-Message-State: AAQBX9cAhospyjiUw6e6YjlORAvLUKeG3CUJXHC5Le6u/OcTzMGcVQY4 vOPTj7NuLSv+nRoeQnigCho= X-Google-Smtp-Source: AKy350as+uWvZB1UDA0rClSPEJZ9KJctRGU6UJ7yZVRqXBfMpnr1bm8yMh1ziKuQa5ocG0CjKQw7XQ== X-Received: by 2002:adf:ec46:0:b0:2ce:9fb8:b560 with SMTP id w6-20020adfec46000000b002ce9fb8b560mr9761836wrn.8.1682331476919; Mon, 24 Apr 2023 03:17:56 -0700 (PDT) Received: from localhost (host86-156-84-164.range86-156.btcentralplus.com. [86.156.84.164]) by smtp.gmail.com with ESMTPSA id a14-20020adfe5ce000000b002fbe0772ab1sm10448840wrn.16.2023.04.24.03.17.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Apr 2023 03:17:55 -0700 (PDT) Date: Mon, 24 Apr 2023 11:17:55 +0100 From: Lorenzo Stoakes To: Christoph Hellwig Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jason Gunthorpe , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Oleg Nesterov , Jason Gunthorpe Subject: Re: [PATCH v2] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: <90a54439-5d30-4711-8a86-eba816782a66@lucifer.local> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 3syh411cg9g8zt8dqdin6js1kab5omh9 X-Rspamd-Queue-Id: 9332D8000C X-HE-Tag: 1682331478-298066 X-HE-Meta: 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 rt7hnOcl AyLkYA0/3tHUw4KI8smyyRQ//upvUmZpaFiaOI865DSYf3RjyZ4xRJrKo+V5ANTrC7G1BN/gQ/jBe3sdrpKADHS/cIOPCXeQUvDJaYngSsLKVEsdbkVjJFwHMLAeEICSCtkVuM3dAB3scTtH2/nxRaAKtgQBctC9O5fL1S6F64fODZT6LHA9kMPk8D6uDfD91aRcfiJlqNPyEkt1BXYAfuN27FG5/N+ps661r/HY7MK22HTSSZxrV7aCUU8mG3So5PYXCt2ogoiBAYtxYuP5D3fz226xJVAYGMskoItCgkYKmU1o3t4Smfpo02VEuPiXSR2i1e2hNvmxs9qfJlTqcGPJzgze36gUSNzqwvhiKNCfn0PHHOdJw7hTcHE180uUxC4wmuNxVG/nHmxUkt8KSz8XNHqwG+Bb3XxfGVnXwpAiQzNgotimVTzfxI4chzjD0vNWrq1LI09VsXGo= 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 Mon, Apr 24, 2023 at 02:43:56AM -0700, Christoph Hellwig wrote: > I'm pretty sure DIRECT I/O reads that write into file backed mappings > are out there in the wild. > > So while I wish we had never allowed this, the exercise seems futile and > instead we need to work on supporting this usecase, with the FOLL_PIN > infrastructure being a big step toward that. It's not entirely futile, there's at least one specific use case, which is io_uring which is currently open coding an equivalent check themselves. By introducing this change we prevent them from having to do so and provide a means by which other callers who implicitly need this do not have to do so either. In addition, this change frees up a blocked patch series intending to clean up GUP which should help open the door to further improvements across the system. So I would argue certainly not futile. In addition, I think it's useful to explicitly document that this is a broken case and, through use of the flag, highlight places which are problematic (although perhaps not exhaustively). I know Jason is keen on fixing this at a fundamental level and this flag is ultimately his suggestion, so it certainly doesn't stand in the way of this work moving forward.