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 CDECEC00140 for ; Wed, 10 Aug 2022 16:53:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 25F5B6B0071; Wed, 10 Aug 2022 12:53:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 20E518E0002; Wed, 10 Aug 2022 12:53:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0AFC38E0001; Wed, 10 Aug 2022 12:53:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id EC8286B0071 for ; Wed, 10 Aug 2022 12:53:15 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id BA28E14062F for ; Wed, 10 Aug 2022 16:53:15 +0000 (UTC) X-FDA: 79784278350.22.002D02C Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by imf06.hostedemail.com (Postfix) with ESMTP id 5A15E180034 for ; Wed, 10 Aug 2022 16:53:15 +0000 (UTC) Received: from localhost (modemcable141.102-20-96.mc.videotron.ca [96.20.102.141]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: krisman) by madras.collabora.co.uk (Postfix) with ESMTPSA id 4E2A966019C1; Wed, 10 Aug 2022 17:53:13 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1660150394; bh=Dxlub/En694B1OVwDjJc8t0TX0eJ/thQHwv6ZgyAFss=; h=From:To:Cc:Subject:References:Date:In-Reply-To:From; b=T3LUdJuYm6pho9zz3V+Hu1Z+mBuq56NgJIlemP6tGh4klBENeaYswfS6PYiFv9Yv+ LupLBkAsxaJBuY6G+ziP1qBdhiUC0YejOfT99UGZZas8pKf9alnvLGekY4mXkP+PH/ 6H3EyQ7pR/zqWSbrksq4JXrmQ2G3HL6vXbOpp8XjblylzhMdD2rJsBs+UbOEoYDUH9 Q7P2oiY6Ic+dbTYxWxf3dFkwa143H2ke5lfFqYuH8GOmLDxdBOHzvnoz8CPezYwMYz coHlw2dK0qd118LITxpwIQRxH2tkJCSlF0FMS7NnjzLHJ5ExL9oJdpfaNfA2djr4Bk tTO5BA1GQZuPg== From: Gabriel Krisman Bertazi To: Peter.Enderborg@sony.com Cc: Muhammad Usama Anjum , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "H. Peter Anvin" , Arnd Bergmann , Andrew Morton , Peter Zijlstra , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Shuah Khan , "open list:DOCUMENTATION" , open list , "open list:PROC FILESYSTEM" , "open list:ABI/API" , "open list:GENERIC INCLUDE/ASM HEADER FILES" , "open list:MEMORY MANAGEMENT" , "open list:PERFORMANCE EVENTS SUBSYSTEM" , "open list:KERNEL SELFTEST FRAMEWORK" , "kernel@collabora.com" Subject: Re: [PATCH 0/5] Add process_memwatch syscall References: <20220726161854.276359-1-usama.anjum@collabora.com> <456a8052-dfd2-e00c-6da7-fb5aa0c35f2c@sony.com> Date: Wed, 10 Aug 2022 12:53:07 -0400 In-Reply-To: <456a8052-dfd2-e00c-6da7-fb5aa0c35f2c@sony.com> (Peter's message of "Wed, 10 Aug 2022 09:22:02 +0000") Message-ID: <87tu6kghvw.fsf@collabora.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660150395; 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=3mPL2qUYzvfUqO6W4u/JE5PLLnPkmQWsGUIQpFeA8qs=; b=D4IRoj1zJdS5bHDvj7ecuzRSKPULoLUiSo4Q6aixy+gDWCs49cE+KDFpSL/9uY/fPFVcM6 p0rNunhRL44Mbj+rn9FABESI6EPAYpGrYz3jJ+fURJ236ekCyE4p49tslkZMoLOkBuFXaM HeEKkH5k0sjMdMxDwI6u0+xQfequ5sE= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=T3LUdJuY; spf=pass (imf06.hostedemail.com: domain of krisman@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=krisman@collabora.com; dmarc=pass (policy=none) header.from=collabora.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660150395; a=rsa-sha256; cv=none; b=BMl/zxO6w9jvNY/wcr1DZlV8wVzUwxki6ZiPMLxCjrypFsD6s/lXukyY7ARNXCYpboJ2jV 6EtP/jNQ4jENzOj0Gkrc+2T0BE+xbQ4D2o9CHWTr99A/1wJbFctNcek3U0Mps42AsdgqrF QUNY4ulnhJERN+d3LTxel2tAMDid+hc= X-Stat-Signature: 6n7f64twsfgpqdygiatejtj3ycrkofo7 X-Rspamd-Queue-Id: 5A15E180034 Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=T3LUdJuY; spf=pass (imf06.hostedemail.com: domain of krisman@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=krisman@collabora.com; dmarc=pass (policy=none) header.from=collabora.com X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1660150395-45709 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: "Peter.Enderborg@sony.com" writes: >> >> This syscall can be used by the CRIU project and other applications which >> require soft-dirty PTE bit information. The following operations are >> supported in this syscall: >> - Get the pages that are soft-dirty. >> - Clear the pages which are soft-dirty. >> - The optional flag to ignore the VM_SOFTDIRTY and only track per page >> soft-dirty PTE bit >> Hi Peter, (For context, I wrote a previous version of this patch and have been working with Usama on the current patch). > Why can it not be done as a IOCTL? Considering an ioctl is basically a namespaced syscall with extra-steps, surely we can do it :) There are a few reasons we haven't, though: 1) ioctl auditing/controling is much harder than syscall 2) There is a concern for performance, since this might be executed frequently by windows applications running over wine. There is an extra cost with unnecessary copy_[from/to]_user that we wanted to avoid, even though we haven't measured. 3) I originally wrote this at the time process_memadvise was merged. I felt it fits the same kind of interface exposed by process_memadvise/process_mrelease, recently merged. 4) Not obvious whether the ioctl would be against pagemap/clear_refs. Neither file name describes both input and output semantics. Obviously, all of those reasons can be worked around, and we can turn this into an ioctl. Thanks, -- Gabriel Krisman Bertazi