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Tue, 28 May 2024 20:20:52 -0700 Date: Tue, 28 May 2024 20:20:50 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: Jason Gunthorpe , "will@kernel.org" , "robin.murphy@arm.com" , "suravee.suthikulpanit@amd.com" , "joro@8bytes.org" , "linux-kernel@vger.kernel.org" , "iommu@lists.linux.dev" , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "Liu, Yi L" , "eric.auger@redhat.com" , "vasant.hegde@amd.com" , "jon.grimm@amd.com" , "santosh.shukla@amd.com" , "Dhaval.Giani@amd.com" , "shameerali.kolothum.thodi@huawei.com" Subject: Re: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl Message-ID: References: <20240524131912.GT20229@nvidia.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL6PEPF0001AB53:EE_|CH3PR12MB9121:EE_ X-MS-Office365-Filtering-Correlation-Id: ea5b4631-7ccb-46c5-e081-08dc7f8e61ad X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230031|82310400017|7416005|376005|1800799015|36860700004; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, May 29, 2024 at 02:58:11AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Wednesday, May 29, 2024 4:23 AM > > What I mean is for regular vSMMU. Without VCMDQ, a regular vSMMU > > on a multi-pSMMU setup will look like (e.g. three devices behind > > different SMMUs): > > |<------ VMM ------->|<------ kernel ------>| > > |-- viommu0 --|-- pSMMU0 --| > > vSMMU--|-- viommu1 --|-- pSMMU1 --|--s2_hwpt > > |-- viommu2 --|-- pSMMU2 --| > > > > And device would attach to: > > |<---- guest ---->|<--- VMM --->|<- kernel ->| > > |-- dev0 --|-- viommu0 --|-- pSMMU0 --| > > vSMMU--|-- dev1 --|-- viommu1 --|-- pSMMU1 --| > > |-- dev2 --|-- viommu2 --|-- pSMMU2 --| > > > > When trapping a device cache invalidation: it is straightforward > > by deciphering the virtual device ID to pick the viommu that the > > device is attached to. > > I understand how above works. > > My question is why that option is chosen instead of going with 1:1 > mapping between vSMMU and viommu i.e. letting the kernel to > figure out which pSMMU should be sent an invalidation cmd to, as > how VT-d is virtualized. > > I want to know whether doing so is simply to be compatible with > what VCMDQ requires, or due to another untold reason. Because we use viommu as a VMID holder for SMMU. So a pSMMU must have its own viommu to store its VMID for a shared s2_hwpt: |-- viommu0 (VMIDx) --|-- pSMMU0 --| vSMMU--|-- viommu1 (VMIDy) --|-- pSMMU1 --|--s2_hwpt |-- viommu2 (VMIDz) --|-- pSMMU2 --| Thanks Nicolin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel