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Sun, 2 Mar 2025 08:05:24 +0000 Message-ID: <13e1e1d8-5870-44ea-a800-e5b25bafd344@intel.com> Date: Sun, 2 Mar 2025 16:10:46 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] iommu/amd: Add Secure ATS support To: Vasant Hegde , "Tian, Kevin" , Jason Gunthorpe CC: Robin Murphy , "iommu@lists.linux.dev" , "joro@8bytes.org" , "will@kernel.org" , "suravee.suthikulpanit@amd.com" References: <20250225105829.52223-1-vasant.hegde@amd.com> <20250225145518.GJ545008@ziepe.ca> <20250226011750.GB5011@ziepe.ca> <4fba254e-ca47-4e7b-baf3-0228d9605c2b@amd.com> <942a1a66-5c18-43e2-886e-df38cb3e7258@intel.com> <54db17d7-b150-4579-a33d-f1b5cc8943bc@amd.com> <6eb0ec90-5859-4605-8a2e-657f6f711d61@intel.com> <825ddadd-6770-46b5-936e-f17988534984@amd.com> Content-Language: en-US From: Yi Liu In-Reply-To: <825ddadd-6770-46b5-936e-f17988534984@amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SI2PR04CA0007.apcprd04.prod.outlook.com (2603:1096:4:197::19) 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_|MN6PR11MB8196:EE_ X-MS-Office365-Filtering-Correlation-Id: 23a4f7ab-3cc0-45d8-26ab-08dd5960fc56 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7053199007; 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They are functionally different but serving the same purpose >>>>>>>> to the user. From user p.o.v. it's sufficient to have a general flag for >>>>>>>> sats >>>>>>>> when allocating a domain. The underlying driver decides whether such >>>>>>>> flag is supported based on the domain type and the associated device, >>>>>>>> just like checks on other existing flags. >>>>>>>> >>>>>>> >>>>>>> Chatted with Yi offline. Having untrusted user control a security >>>>>>> feature doesn't make much sense. Probably what we really require >>>>>>> is: >>>>>>> >>>>>>> - IOMMU core exposes a separate sats knob per probed device, >>>>>>>     allowing the administrator to manage the sats policy which could >>>>>>>     be no ats, unsecure ats and secure ats (might be further set per >>>>>>>     domain type in case the hw doesn't support sats for all types or >>>>>>>     the driver doesn't support all hw-supported types in one batch). >>>>>> >>>>>> When you say "sats knob", you mean sysfs interface? >>>>> >>>>> yes >>>> >>>> in case this is the direction. This might be a per iommu_group knob. do we >>> >>> >>>> want a default value per some info that can be probed by kernel? >>> >>> I prefer kernel probe/setting default values so that we can enforce HW >>> restrictions (like SNP, untrusted device etc) and then.... >> >> I got untrusted device. How is SNP probed? Is there any bit for it? > > Yes. There is a IOMMU feature bit. see iommu_snp_enable(). sure. I'm also thinking about the impact of such a knob. How should we define this knob. Should we allow it to disable/enable ATS? Especially in runtime. e.g. if the device is identified to be ATS untrusted by the admin, while the hw does not support SATS, it seems reasonable to disable ATS for such device. This might change the driver behavior on ATS enabling. Intel iommu driver enables ATS as long as it's available in the probe_device() op. What about AMD and ARM? On the other hand, we may just define the knob as sats required or not. This is just a knob to let kernel know if the iommu driver needs to enable sats or not. While leave the ATS enabling policy unchanged. This means we need to probe the sats capability of iommu hw before creating the knob in sysfs. Any ideas? -- Regards, Yi Liu