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Howlett" , Vlastimil Babka , Jann Horn , Shuah Khan , David Hildenbrand , =?utf-8?Q?Miko=C5=82aj?= Lenczewski , Mark Rutland , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v1 1/2] mm: Clear uffd-wp PTE/PMD state on mremap() Message-ID: <9221000a-161b-46ea-a065-ee339837aacb@lucifer.local> References: <20250107144755.1871363-1-ryan.roberts@arm.com> <20250107144755.1871363-2-ryan.roberts@arm.com> <26ee9ae0-405f-4085-a864-48d1ee6371f1@arm.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: LO4P265CA0079.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:2bd::12) To BYAPR10MB3366.namprd10.prod.outlook.com (2603:10b6:a03:14f::25) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB3366:EE_|LV8PR10MB7847:EE_ X-MS-Office365-Filtering-Correlation-Id: c2d5264a-dbfe-4611-684c-08dd358a4bbc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014; 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This mismatch causes a subsequent mprotect(PROT_WRITE) > > > to trigger a warning in page_table_check_pte_flags() due to setting the > > > pte to writable while uffd-wp is still set. > > > > > > Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any > > > such mremap() so that the values are consistent with the existing > > > clearing of VM_UFFD_WP. Be careful to clear the logical flag regardless > > > of its physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover > > > PTE, huge PMD and hugetlb paths. > > > > I just noticed that Andrew sent this to Linus and it's now in his tree; I'm > > suddenly very nervous that it doesn't have any acks. I don't suppose you would > > be able to do a quick review to calm the nerves?? > > Heh, I fully trusted you, and I appreciated your help too. I'll need to run > for 1-2 hours, but I'll read it this afternoon. > > Side note: no review is as good as tests on reliability POV if that was the > concern, but I'll try my best. Things go all inception though when part of the review _are_ the tests ;) Though of course there are also all existing uffd tests and the bots that add a bit of weight. This isn't really my area so will defer to Peter on the review side. I sort of favour putting hotfixes in quick, but this one has gone in quicker than some reviewed hotfixes which we left in unstable... however towards the end of a cycle I think Andrew is stuck between a rock and a hard place in deciding how to handle these. So I'm guessing the heuristic is 'allow to simmer in unstable if time permits in cycle', if known 'good egg' + no objection + towards end of cycle + hotfix - send. I do wonder whether we should require review on hotfixes generally. But then of course that creates rock + hard place decision for Andrew as to whether it gets deferred to the next cycle + stable backports... Maybe one to discuss at LSF? > > Thanks, > > -- > Peter Xu >