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Shutemov" , "x86@kernel.org" , "Tian, Kevin" , "Pei Li" , David Wang <00107082@163.com>, Bert Karwatzki , Sergey Senozhatsky Subject: Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region Message-ID: Reply-To: Yan Zhao References: <1a0884cb-39ed-455e-a505-7c1b2a0e5225@redhat.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1a0884cb-39ed-455e-a505-7c1b2a0e5225@redhat.com> X-ClientProxiedBy: SG2PR06CA0228.apcprd06.prod.outlook.com (2603:1096:4:68::36) To DS7PR11MB5966.namprd11.prod.outlook.com (2603:10b6:8:71::6) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR11MB5966:EE_|DM6PR11MB4516:EE_ X-MS-Office365-Filtering-Correlation-Id: fd4c02e5-c5aa-4dc4-347f-08dcaa19c83b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?f8/fu4J7WsB13TTtKcZiFL5pfHmqZMnZO/ymQEUGhARaj3o2ciAgy+2nHRLg?= =?us-ascii?Q?lInLar0EYCbw+JB9z12tbp3OT/Z9nhEVqNG1kv2DKEODRPySOmR1rUbTJ2CW?= =?us-ascii?Q?VeBmoCj6MLV7F9fJH+tmRJN7WDVGFHKns4Kb1+MaU+2RsPPPxtTIumB3WHDG?= =?us-ascii?Q?ucCeDiTqXBW0TainZW0E6hPbZXzCL2clnWYb1crXCH9uj6Jp+UImzQJcR9JJ?= =?us-ascii?Q?N//eE0Ge4sGmjzFJ+7WOLUMkLTxBXvQjR2jJua//97d9zmJgX+B1MO4pBOYN?= =?us-ascii?Q?qz3xVynej+gy+IVu7Wa6BuTPPiutm4neaqLxZiQ9Zzv6+mB4ywgQuT4zs51f?= =?us-ascii?Q?+pma1ixWz5Apphidx6zu0K1cLG1v2Kds4szD9/F6hokieIjszswTfX4sKlKQ?= =?us-ascii?Q?VXnXbdbgqbvSXXXf+U2iYwsSbl9NK8380ZU6RMl/7+VNjeewOJ8fPQCjXDVz?= =?us-ascii?Q?kAI2dqHTMigf/RHV+vF2wKx1DknFnqykjEpKyhEILeqn61U5kthwF6MDPDRA?= =?us-ascii?Q?NUIgZv3dvRgHNzDBMX/NaLRM08OE8o6LhBpqD2dmVKYW+IYbPHV2WDAZA9D5?= =?us-ascii?Q?HKmCBNdMf6buA76we6Xa97NjfTu5ElCpsDxEGu82hqYFkjzADUewBQh/1yx3?= =?us-ascii?Q?WnA7GJHZZ9hbEbeWcaakd9SuJIQnjyiPseb/CnUU631FNNpRISmc3fHnhIms?= =?us-ascii?Q?QSV5A1vKsKt3tnLvRyWwf0KC6Wwo0ntKnPHUCdNoBNpDX5M9IyVjU/KEnxfe?= =?us-ascii?Q?KSE4w7Sp0+0VEQNbeRNgiBWaBlsivtAlznGsP0OCEf7YDQ8zAyC7BoQ+viHQ?= =?us-ascii?Q?8WX+21H+o6/TQq+j/NK4qHwL87sqqjzDPIQVZ+hTOLISDRb/nxAGlWag3BRj?= =?us-ascii?Q?EmAO/mCjA4TZGgGEGeVHPhoMdJcFmPlag7otGJZ7EId8Ntn5TfDuzLmyWVDs?= =?us-ascii?Q?bvJyAy5nSDYNrk9WvXUf5nK+IgHSLdN75Vm9IJNLWzsp36o7bylT6H2g7ljp?= =?us-ascii?Q?4P15ShV5B3AHzKULhlomOek/F7QPpTw3B69StcfFWgqwzKo8mT0EjA15EeuD?= =?us-ascii?Q?YsrQ/i6m7bLbR0eXsG38GDMc290ylv1yhPUdaAAsBrF+3xiVk3lClwh8lVsY?= =?us-ascii?Q?x5jk0xwr6XmAIlEqlTAR1z+7A/gkPNtM47tJKLm9jOYRleIqi6ZcVo36oVSZ?= =?us-ascii?Q?JV5Vs/aCJIEc4pXuKz/EX7AVDCLJoCZuPRfMAzqPm7y3mnY++q7AlD+lrhHA?= =?us-ascii?Q?Ys/ODqDFtQBS7cWdXrO3ngUv5qTr3F/vLeaEBnYCOh4VqUGCZMdH/529tyg6?= =?us-ascii?Q?RaPJIdDV971E5sPWfJHh9PQQTXioB3JPmroibLofWL9LOg=3D=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DS7PR11MB5966.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(7416014)(1800799024)(366016);DIR:OUT;SFP:1101; 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Then if we have two sets of pfns, then we can > > > > 1. Call remap_pfn_range() in mmap() for pfn set 1. > > > > > > I don't think this will work.. At least from the current implementation, > > > remap_pfn_range() will only reserve the memtype if the range covers the > > > whole vma. > > Hmm, by referring to pfn set 1 and pfn set 2, I mean that they're both > > covering the entire vma, but at different times. > > > > To make it more accurately: > > > > Consider this hypothetical scenario (not the same as what's implemented in > > vfio-pci, but seems plausible): > > > > Suppose we have a vma covering only one page, then > > (1) Initially, the vma is mapped to pfn1, with remap_pfn_range(). > > (2) Subsequently, unmap_single_vma() is invoked to unmap the entire VMA. > > (3) The driver then maps the entire vma to pfn2 in fault handler > > > > Given this context, my questions are: > > 1. How can we reserve the memory type for pfn2? Should we call > > track_pfn_remap() in mmap() in advance? > > 2. How do we untrack the memory type for pfn1 and pfn2, considering they > > belong to the same VMA but mutual exclusively and not concurrently? > > Do we really have to support such changing PFNs in a VMA? Are there existing > use cases that would rely on that? I don't know. But it's not disallowed. > Would it be a problem if we would merge the mmap+track_pfn_remap, such that > such a special VMA can only ever belong to a single PFN range, that is > fixed, but PFNs can be faulted in lazily? If we allow a fixed PFN range to be faulted in lazily to different physical PFNs, looks we can't rely on track_pfn_remap() in mmap() and untrack_pfn() in unmap_vmas() to reserve/untrack memtypes.