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Wysocki" , Robert Moore , Robin Murphy , Sudeep Holla , Will Deacon , Alex Williamson , Eric Auger , Jean-Philippe Brucker , Moritz Fischer , Michael Shavit , Nicolin Chen , "patches@lists.linux.dev" Subject: Re: [PATCH v2 6/8] iommu/arm-smmu-v3: Support IOMMU_GET_HW_INFO via struct arm_smmu_hw_info Message-ID: <20240904120103.GB3915968@nvidia.com> References: <0-v2-621370057090+91fec-smmuv3_nesting_jgg@nvidia.com> <6-v2-621370057090+91fec-smmuv3_nesting_jgg@nvidia.com> <20240830171602.GX3773488@nvidia.com> <20240903001654.GE3773488@nvidia.com> <20240903234019.GI3773488@nvidia.com> <9e8153c95b664726bd7fcb6d0605610a@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9e8153c95b664726bd7fcb6d0605610a@huawei.com> X-ClientProxiedBy: MN2PR04CA0022.namprd04.prod.outlook.com (2603:10b6:208:d4::35) To CH3PR12MB7763.namprd12.prod.outlook.com (2603:10b6:610:145::10) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR12MB7763:EE_|PH8PR12MB6794:EE_ X-MS-Office365-Filtering-Correlation-Id: 865fc5a9-7054-4fe5-95d1-08dcccd9408a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024|7416014; 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It also depends on whether the > VMM has requested sve for a specific Guest or not(Qemu has option to > turn sve on/off, similarly pmu as well). Based on that KVM > populates the Guest specific ID registers. And Guest /proc/cpuinfo > reflects that. > > And for some features if KVM is not handling the feature properly or > not making any sense to be exposed to Guest, those features are > masked in ID registers. > > Recently ARM64 ID registers has been made writable from userspace to > allow VMM to turn on/off features, so that VMs can be migrated > between hosts that differ in feature support. > > https://lore.kernel.org/all/ZR2YfAixZgbCFnb8@linux.dev/T/#m7c2493fd2d43c13a3336d19f2dc06a89803c6fdb I see, so there is a significant difference - in KVM the kernel controls what ID values the VM observes and in vSMMU the VMM controls it. Jason