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Wed, 11 Sep 2024 00:40:57 -0700 Date: Wed, 11 Sep 2024 00:40:55 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "jgg@nvidia.com" , "will@kernel.org" , "joro@8bytes.org" , "suravee.suthikulpanit@amd.com" , "robin.murphy@arm.com" , "dwmw2@infradead.org" , "baolu.lu@linux.intel.com" , "shuah@kernel.org" , "linux-kernel@vger.kernel.org" , "iommu@lists.linux.dev" , "linux-arm-kernel@lists.infradead.org" , "linux-kselftest@vger.kernel.org" , "eric.auger@redhat.com" , "jean-philippe@linaro.org" , "mdf@kernel.org" , "mshavit@google.com" , "shameerali.kolothum.thodi@huawei.com" , "smostafa@google.com" , "Liu, Yi L" Subject: Re: [PATCH v2 00/19] iommufd: Add VIOMMU infrastructure (Part-1) Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001F6:EE_|SN7PR12MB7132:EE_ X-MS-Office365-Filtering-Correlation-Id: b130abf8-9a2d-4438-106c-08dcd2351793 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|82310400026|376014|1800799024|7416014; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Sep 2024 07:41:05.0225 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b130abf8-9a2d-4438-106c-08dcd2351793 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.233];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF000001F6.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB7132 On Wed, Sep 11, 2024 at 07:18:10AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Wednesday, September 11, 2024 3:08 PM > > > > On Wed, Sep 11, 2024 at 06:12:21AM +0000, Tian, Kevin wrote: > > > > From: Nicolin Chen > > > > Sent: Wednesday, August 28, 2024 1:00 AM > > > > > > > [...] > > > > On a multi-IOMMU system, the VIOMMU object can be instanced to the > > > > number > > > > of vIOMMUs in a guest VM, while holding the same parent HWPT to > > share > > > > the > > > > > > Is there restriction that multiple vIOMMU objects can be only created > > > on a multi-IOMMU system? > > > > I think it should be generally restricted to the number of pIOMMUs, > > although likely (not 100% sure) we could do multiple vIOMMUs on a > > single-pIOMMU system. Any reason for doing that? > > No idea. But if you stated so then there will be code to enforce it e.g. > failing the attempt to create a vIOMMU object on a pIOMMU to which > another vIOMMU object is already linked? Yea, I can do that. > > > > stage-2 IO pagetable. Each VIOMMU then just need to only allocate its > > own > > > > VMID to attach the shared stage-2 IO pagetable to the physical IOMMU: > > > > > > this reads like 'VMID' is a virtual ID allocated by vIOMMU. But from the > > > entire context it actually means the physical 'VMID' allocated on the > > > associated physical IOMMU, correct? > > > > Quoting Jason's narratives, a VMID is a "Security namespace for > > guest owned ID". The allocation, using SMMU as an example, should > > the VMID alone is not a namespace. It's one ID to tag another namespace. > > > be a part of vIOMMU instance allocation in the host SMMU driver. > > Then, this VMID will be used to mark the cache tags. So, it is > > still a software allocated ID, while HW would use it too. > > > > VMIDs are physical resource belonging to the host SMMU driver. Yes. Just the lifecycle of a VMID is controlled by a vIOMMU, i.e. the guest. > but I got your original point that it's each vIOMMU gets an unique VMID > from the host SMMU driver, not exactly that each vIOMMU maintains > its own VMID namespace. that'd be a different concept. What's a VMID namespace actually? Please educate me :) Thanks Nicolin