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Wed, 4 Sep 2024 10:29:28 -0700 Date: Wed, 4 Sep 2024 10:29:26 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Baolu Lu , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 02/19] iommufd/viommu: Add IOMMUFD_OBJ_VIOMMU and IOMMU_VIOMMU_ALLOC ioctl Message-ID: References: <55918c41-65c4-435c-860b-b2a177b0d364@linux.intel.com> <20240904162621.GN3915968@nvidia.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20240904162621.GN3915968@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF00003444:EE_|DS7PR12MB8201:EE_ X-MS-Office365-Filtering-Correlation-Id: 08895347-1911-4595-b5a8-08dccd072b0e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|376014|1800799024|7416014|82310400026; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Sep 2024 17:29:44.9054 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 08895347-1911-4595-b5a8-08dccd072b0e X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DS2PEPF00003444.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB8201 On Wed, Sep 04, 2024 at 01:26:21PM -0300, Jason Gunthorpe wrote: > On Sun, Sep 01, 2024 at 10:27:09PM -0700, Nicolin Chen wrote: > > On Sun, Sep 01, 2024 at 10:39:17AM +0800, Baolu Lu wrote: > > > On 2024/8/28 0:59, Nicolin Chen wrote: > > > > +int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd) > > > > +{ > > > > + struct iommu_viommu_alloc *cmd = ucmd->cmd; > > > > + struct iommufd_hwpt_paging *hwpt_paging; > > > > + struct iommufd_viommu *viommu; > > > > + struct iommufd_device *idev; > > > > + int rc; > > > > + > > > > + if (cmd->flags) > > > > + return -EOPNOTSUPP; > > > > + > > > > + idev = iommufd_get_device(ucmd, cmd->dev_id); > > > > > > Why does a device reference count is needed here? When is this reference > > > count released after the VIOMMU is allocated? > > > > Hmm, it was used to get dev->iommu->iommu_dev to pin the VIOMMU to > > a physical IOMMU instance (in v1). Jason suggested to remove that, > > yet I didn't realize that this idev is now completely useless. > > > > With that being said, a parent HWPT could be shared across VIOMUs > > allocated for the same VM. So, I think we do need a dev pointer to > > know which physical instance the VIOMMU allocates for, especially > > for a driver-managed VIOMMU. > > Eventually you need a way to pin the physical iommu, without pinning > any idevs. Not sure how best to do that Just trying to clarify "without pinning any idevs", does it mean we shouldn't pass in an idev_id to get dev->iommu->iommu_dev? Otherwise, iommu_probe_device_lock and iommu_device_lock in the iommu.c are good enough to lock dev->iommu and iommu->list. And I think we just need an iommu helper refcounting the dev_iommu (or iommu_device) as we previously discussed. Thanks Nicolin