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Received: from CH3PR12MB9194.namprd12.prod.outlook.com (2603:10b6:610:19f::7) by PH7PR12MB8779.namprd12.prod.outlook.com (2603:10b6:510:26b::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8005.27; Tue, 1 Oct 2024 05:07:10 +0000 Received: from CH3PR12MB9194.namprd12.prod.outlook.com ([fe80::53fb:bf76:727f:d00f]) by CH3PR12MB9194.namprd12.prod.outlook.com ([fe80::53fb:bf76:727f:d00f%4]) with mapi id 15.20.8005.026; Tue, 1 Oct 2024 05:07:10 +0000 Message-ID: <3414d639-50b7-4175-abb4-b3d87f5744f0@amd.com> Date: Tue, 1 Oct 2024 15:06:57 +1000 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH v2 00/19] iommufd: Add VIOMMU infrastructure (Part-1) Content-Language: en-US To: Nicolin Chen Cc: "Tian, Kevin" , "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" References: From: Alexey Kardashevskiy In-Reply-To: Content-Type: text/plain; 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Any reason for doing that? >> >> >> Just to clarify the terminology here - what are pIOMMU and vIOMMU exactly? >> >> On AMD, IOMMU is a pretend-pcie device, one per a rootport, manages a DT >> - device table, one entry per BDFn, the entry owns a queue. A slice of >> that can be passed to a VM (== queues mapped directly to the VM, and >> such IOMMU appears in the VM as a pretend-pcie device too). So what is >> [pv]IOMMU here? Thanks, > > The "p" stands for physical: the entire IOMMU unit/instance. In > the IOMMU subsystem terminology, it's a struct iommu_device. It > sounds like AMD would register one iommu device per rootport? Yup, my test machine has 4 of these. > The "v" stands for virtual: a slice of the pIOMMU that could be > shared or passed through to a VM: > - Intel IOMMU doesn't have passthrough queues, so it uses a > shared queue (for invalidation). In this case, vIOMMU will > be a pure SW structure for HW queue sharing (with the host > machine and other VMs). That said, I think the channel (or > the port) that Intel VT-d uses internally for a device to > do a two-stage translation can be seen as a "passthrough" > feature, held by a vIOMMU. > - AMD IOMMU can assign passthrough queues to VMs, in which > case, vIOMMU will be a structure holding all passthrough > resource (of the pIOMMU) assisgned to a VM. If there is a > shared resource, it can be packed into the vIOMMU struct > too. FYI, vQUEUE (future series) on the other hand will > represent each passthrough queue in a vIOMMU struct. The > VM then, per that specific pIOMMU (rootport?), will have > one vIOMMU holding a number of vQUEUEs. > - ARM SMMU is sort of in the middle, depending on the impls. > vIOMMU will be a structure holding both passthrough and > shared resource. It can define vQUEUEs, if the impl has > passthrough queues like AMD does. > > Allowing a vIOMMU to hold shared resource makes it a bit of an > upgraded model for IOMMU virtualization, from the existing HWPT > model that now looks like a subset of the vIOMMU model. Thanks for confirming. I've just read in this thread that "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?"? thought "we have every reason to do that, unless p means something different", so I decided to ask :) Thanks, > > Thanks > Nicolin -- Alexey