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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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240904_182956_748179_9BCA9A06 X-CRM114-Status: GOOD ( 22.12 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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