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Mon, 15 Jul 2024 08:42:17 +0000 Message-ID: Date: Mon, 15 Jul 2024 16:46:12 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] iommu_ops->domain_alloc_paging() enhancement to support AMD IOMMU driver To: Robin Murphy , Jason Gunthorpe CC: Vasant Hegde , Joerg Roedel , "iommu@lists.linux.dev" , Suravee Suthikulpanit , Will Deacon , Baolu Lu References: <7e249bc6-c578-40f0-aca7-835149a0ad39@amd.com> <20240628130330.GY791043@ziepe.ca> <26524622-971f-47f5-936e-d0173d342288@amd.com> <1f8f04e5-3b70-45de-bd93-e3c96fb0a555@amd.com> <68d300af-4d3d-497e-9338-d99dbf88dd21@amd.com> <8bfc6cb7-d2d7-4d4c-9970-f4f207fb54b4@intel.com> <20240709182303.GK14050@ziepe.ca> <3eff5c86-8b5d-491a-955e-794198350ec3@intel.com> <20240711234917.GW14050@ziepe.ca> <35ff9f32-ae60-4124-9ced-42f82c2b4f93@arm.com> Content-Language: en-US From: Yi Liu In-Reply-To: <35ff9f32-ae60-4124-9ced-42f82c2b4f93@arm.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SI2PR04CA0006.apcprd04.prod.outlook.com (2603:1096:4:197::13) To DS0PR11MB7529.namprd11.prod.outlook.com (2603:10b6:8:141::20) Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7529:EE_|SA0PR11MB4637:EE_ X-MS-Office365-Filtering-Correlation-Id: 671190eb-3145-4aba-22ee-08dca4aa083c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014; 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For AMD, can a single device be attached to multiple V1 page table? >>>>> IIRC. looks like AMD has only one V1 page table pointer per BDF. But >>>>> there >>>>> is a PASID table which has multiple cr3 page table pointers. >>>> >>>> Yes, ARM and AMD both have kinds of iommu_domains that cannot be >>>> attached to a PASID. >>> >>> I see. VT-d does not have such a limitation AFAIK. >> >> Yeah, it is nice for software that VT-d put the right bits in to let >> all paths select either format. >> >>> BTW. SVA domain shall not be attached to RID I suppose. This should >>> be a common restriction across vendors. Do you think it is valuable >>> to let iommu core block such an attempt? >> >> Yeah, maybe. > > There's no functional reason to disallow it for Arm SMMUs, at least, so > it's something that could potentially want relaxing back to per-driver in > future. I've heard murmurings over the years about potential use-cases for > SVA with platform and/or non-PASID PCI devices, but never anything concrete > for existing hardware. I imagine we can expect to see more SVA-interested > on-chip accelerators in future, but whether they'll all be nice and support > Substreams (i.e. "platform PASIDs") is the question... I see. Then let's keep the core as it is now. -- Regards, Yi Liu