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 15127C3DA7D for ; Wed, 28 Dec 2022 14:14:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232771AbiL1OOX (ORCPT ); Wed, 28 Dec 2022 09:14:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55542 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229627AbiL1OOV (ORCPT ); Wed, 28 Dec 2022 09:14:21 -0500 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5BF3B9FFC for ; Wed, 28 Dec 2022 06:14:20 -0800 (PST) Received: from [192.168.10.12] (unknown [39.45.24.179]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id EF0A96601F12; Wed, 28 Dec 2022 14:14:14 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1672236857; bh=mz8NzyzkbjYu2yLpQyz2BB2V5QZ0YMUvPPqxgxNxV5c=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=JMCNsn5TxeR9brY7LnaGMEeaKPLn6bspPpFQ4aSuZvnwTnecTxtl7FsZcPDq4YXON pfLDTvuxKhbrNH9FW3JUZJ9hIc5/unWs9t7ud8OSIfRgCVjIPpYEJXHP8iAS70CbNt yLMpLTMUCnbC3V9r/zDPExw8IypwmAyNGRR0pdqkwi3d9ox0lvvRx3p7xBfZX+oxog C1ffEubsut80Jcqq8qmFuIcmtpGIMH/qDrK89Zb6aMTdLABjfefHpwIVB1/YZKu3JC LrEI0KQ5tZqUn6rT0JevnUbElyhOfhO7BLJpt7KVouG0fEVHAl807hM/Lmd0jngpiX Ke71rZ4j7jajA== Message-ID: <40cc5f89-fa10-e107-671e-84bdcf7a4430@collabora.com> Date: Wed, 28 Dec 2022 19:14:09 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Cc: Muhammad Usama Anjum , Nadav Amit , Andrea Arcangeli , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel@collabora.com, Peter Xu , David Hildenbrand , Paul Gofman Subject: Re: [PATCH v4 1/3] mm/mprotect: Fix soft-dirty check in can_change_pte_writable() To: Cyrill Gorcunov , Andrew Morton References: <20220725142048.30450-1-peterx@redhat.com> <20220725142048.30450-2-peterx@redhat.com> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/19/22 5:19 PM, Muhammad Usama Anjum wrote: > Addition of vma_soft_dirty_enabled() has tinkered with the soft-dirty PTE > bit status setting. The internal behavior has changed. The test case was > shared by David > (https://lore.kernel.org/all/bfcae708-db21-04b4-0bbe-712badd03071@redhat.com/). > The explanation is as following: > > _Before_ addition of this patch(76aefad628aae), > m = mmap(2 pages) > clear_softdirty() > mremap(m + pag_size) > mprotect(READ) > mprotect(READ | WRITE); > memset(m) > After memset(), > PAGE-1 PAGE-2 > VM_SOFTDIRTY set set > PTE softdirty flag set set > /proc//pagemap view set set > > > _After_ addition of this patch(76aefad628aae) > m = mmap(2 pages) > clear_softdirty() > mremap(m + page_size) > mprotect(READ) > mprotect(READ | WRITE); > memset(m) > After memset(), > PAGE-1 PAGE-2 > VM_SOFTDIRTY set set > PTE softdirty flag *not set* set > /proc//pagemap view set set > > The user's point of view hasn't changed. But internally after this patch, > the soft-dirty tracking in PTEs gets turn off if VM_SOFTDIRTY is set. The > soft-dirty tracking in the PTEs shouldn't be just turned off when mprotect > is used. Why? Because soft-dirty tracking in the PTEs is always enabled > regardless of VM_SOFTDIRTY is set or not. Example: > > m = mem(2 pages) > At this point: > PAGE-1 PAGE-2 > VM_SOFTDIRTY set set > PTE softdirty flag not set not set > /proc//pagemap view set set > memset(m) > At this point: > PAGE-1 PAGE-2 > VM_SOFTDIRTY set set > PTE softdirty flag set set > /proc//pagemap view set set > > This example proves that soft-dirty flag on the PTE is set regardless of > the VM_SOFTDIRTY. Hi Andrew and Cyrill, Peter doesn't agree with me here that this change in behavior should be reverted etc. Please comment. -- BR, Muhammad Usama Anjum