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 91DAEC7EE20 for ; Mon, 24 Apr 2023 23:27:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232256AbjDXX1U (ORCPT ); Mon, 24 Apr 2023 19:27:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231543AbjDXX1R (ORCPT ); Mon, 24 Apr 2023 19:27:17 -0400 Received: from mail-wm1-x331.google.com (mail-wm1-x331.google.com [IPv6:2a00:1450:4864:20::331]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 52CC8AF19; Mon, 24 Apr 2023 16:26:38 -0700 (PDT) Received: by mail-wm1-x331.google.com with SMTP id 5b1f17b1804b1-3f1950f569eso24424755e9.2; Mon, 24 Apr 2023 16:26:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1682378787; x=1684970787; 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=dxcDkLWArFVGxXFjJV1x9Mo2OcABMU93AnXLMQRENu4=; b=c2TG5nuleMll1lOBF+XEICpEXvEsyXZQd4wVbiThL4heUkDk9VL44B5Rc1yrKyCnWB Cci1nvmPgz8YXTeygn2yS5Ocu0QGagMQAystMMjPtt4Tj3L+K/FjytNKbAWpaK9lzZKs 8olcJsWqRyr92H7z8CBxcwdDaGTGNJv/MVVSGKdTDaSl0nZqacgLm6RUvLXXN8duB3A/ dWcsBVGAPO3OHq4dksLEzBiRPmrtdC9Cx92HaDamEnGIcawGcBY4pyjzIADaOKRzYmNU Ay0T4FT8uiDo9il2R/9uafQ4R6XwKWbRhcRjMyBGruUYd6XT1PrnxdierIHLUGalpyGA QO+g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1682378787; x=1684970787; 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=dxcDkLWArFVGxXFjJV1x9Mo2OcABMU93AnXLMQRENu4=; b=bk+dGvA+EptHmrX1gwnGyPbrg94BczownDpZEpQPNfNiQZdelHHA4dKDjyNQBhP0Pl p4R6/119N/4u0bauwRX4zNnWV6TxysorfP1R4rJAUiMVhn7nC6wXnJEuoE36M7MbMLqH HsF8+1dMpgNjIMjX82/+zVIxumzQPOusdKnHlbQprb4LM3/Ml1MObU4mSdqpZ9UDYgv7 Dr1yVg1eF4we47E6NI1wdxVZLT2l/QV26N3l+EKylzRhOeottL4fiEO/OMuMhYphPmjZ dmQ6Q3FiDTDWCf0EmbfwknWfdigFVZfJ0WWjVdJg9E6HReWCtjNmgY9PXySoWoCgX7/9 EhKw== X-Gm-Message-State: AAQBX9cTbtTQ5JxlQyQ3oyNoGCDm4vyt6vIECH7mErVlEHTO3zWFt4xG vWY/aw8l6i9USvhqXwWv61Q= X-Google-Smtp-Source: AKy350YmwGfgqMWEg5TF8ScWD6s70vEkQPfSE8eO5Ql2sSUhDXrK+9lnC0X0xiqHMd3x63H/ACYBZg== X-Received: by 2002:a05:600c:3657:b0:3f0:4734:bef8 with SMTP id y23-20020a05600c365700b003f04734bef8mr8467694wmq.39.1682378787397; Mon, 24 Apr 2023 16:26:27 -0700 (PDT) Received: from localhost (host86-156-84-164.range86-156.btcentralplus.com. [86.156.84.164]) by smtp.gmail.com with ESMTPSA id p13-20020a7bcc8d000000b003ee63fe5203sm13343552wma.36.2023.04.24.16.26.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Apr 2023 16:26:26 -0700 (PDT) Date: Tue, 25 Apr 2023 00:26:25 +0100 From: Lorenzo Stoakes To: Jason Gunthorpe Cc: Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , 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 Subject: Re: [PATCH v2] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: References: <4f16b1fc-6bc5-4e41-8e94-151c336fcf69@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 24, 2023 at 08:17:11PM -0300, Jason Gunthorpe wrote: > On Tue, Apr 25, 2023 at 12:03:34AM +0100, Lorenzo Stoakes wrote: > > > Except you dirty a page that is mapped elsewhere that thought everything > > was cleaned and... not sure the PTLs really help you much? > > If we have a writable PTE then while the PTE's PTL is held it is impossible > for a FS to make the page clean as any cleaning action has to also > take the PTL to make the PTE non-present or non-writable. > That's a very good point! Passing things back with a spinlock held feels pretty icky though, and obviously a no-go for a FOLL_PIN. Perhaps for a FOLL_GET this would be workable. > > If we want to be more adventerous the opt-in variant could default to on > > for FOLL_LONGTERM too, but that discussion can be had over on that patch > > series. > > I think you should at least do this too to explain why io_uring code > is moving into common code.. > OK, I'll respin this as a v3 of this series then since we'll be defaulting FOLL_LONGTERM at least (for which there seems to be broad consensus), but also permit this flag to be set manually and set it for io_uring. > Jason