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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 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 7021C1C0014 X-Stat-Signature: apyjb43tfgcdf88kuxu631zto6rr7u9o X-Rspam-User: X-HE-Tag: 1672236859-934630 X-HE-Meta: U2FsdGVkX1+E1t6QZ+zojlHpYteN3UCg5IVX9X3fwl3K6+EMsLyVNSGAUVwnkvvER9eWNbrWTk5XsCfqWSxFM/FPXNBUkdpG4f0wbIeWHx/qc/WpdQx7yIL4hDSgK0Oq7l4jwcuQS3z62yZrhjs74WhAEDnz2Z6qWKHbqYdThiZQb1c/7KrGNV0CF6r00yR9dzEeY4tEm98Gt75MihpoYOG/PdiIcnYLxlw4aP5KtScDx60HL7bVTqvCFhw+yilQuGBF6ZSu/Tuiu+jZSx9ssxcgiY0awwc4jHorB04F+rD1h43d9K35aZUWJr4pGrv3jpl18wo81J0UmcMW8PD4EFzqAJaPU3hJoCja/n56B2I4Pswgu5CCgGHoj4boZKpR03ipveW2FlDJQgRNJviHj84cEFfIWqMk9Gv6dih8Mwa/lLUBWZy3btguQMVDbt13Q0EJUhWmkr7lc44XJnhidnNsEunzp2lr5SdpYqQbNsv0iFr5P/s0J1Yzi9daSmdao0YIh+DKpM8glZ61icxrpTuF4XhKGD1AYs5YGSpXouqQZwofYnFae8wgytPnQXoAzcAXsAQubNNysqiie+dr2DY4pTMez4sko3iPDkmtamYRjMHWyJ5WqhFX5NwBinqS3xqWqBOm92iWQvJPicHR7wpru7WBp0ZpKNnfVidUUKf3wv+hoVTpBZ9Avq89t6XBt8P4XNkcfShpZzdAr24Rz/Q2yImfXCRXtEWSZtLn+JI43EiGJhd788UVCEWsrHBTq3mXqdHT9+g9fwTY7giUYIiE7F1EQeXzVCWV0dbZQdmfAce53dnRvH3sbkpQ7AI13m1M7XuDq1taKXPBQYfGMYmDHlcDriXYIXCZn0Z/ICbv9r2M3/S07y4mKY/De8GIfRPUkrf9Xky4g2oPFkPCbjrpssgHRbxO4ZPtoTxkfAdPHP8EpU2qCi5+aFCY3H26ewyms3Y66Qd4pe9VNhQ WwDQuKry oIWGI1ebjNELCIbcKguWRg6g0shzHiiZrVSV0wieMJ5+pN5H7REsEk08V/w== 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 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