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Thu, 5 Sep 2024 10:53:37 -0700 Date: Thu, 5 Sep 2024 10:53:31 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 10/19] iommufd/viommu: Add vdev_id helpers for IOMMU drivers Message-ID: References: <6ccdfb27c7aa5a5bb7e153165cf90114cae4687c.1724776335.git.nicolinc@nvidia.com> <20240905161415.GS1358970@nvidia.com> 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: <20240905161415.GS1358970@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS3PEPF000099DA:EE_|DS7PR12MB6024:EE_ X-MS-Office365-Filtering-Correlation-Id: dbcc66d1-b66b-4b45-1d9d-08dccdd3bd8d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|7416014|376014|36860700013|1800799024; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Sep 2024 17:54:08.0297 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dbcc66d1-b66b-4b45-1d9d-08dccdd3bd8d 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: DS3PEPF000099DA.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB6024 On Thu, Sep 05, 2024 at 01:14:15PM -0300, Jason Gunthorpe wrote: > On Tue, Aug 27, 2024 at 09:59:47AM -0700, Nicolin Chen wrote: > > Driver can call the iommufd_viommu_find_device() to find a device pointer > > using its per-viommu virtual ID. The returned device must be protected by > > the pair of iommufd_viommu_lock/unlock_vdev_id() function. > > > > Put these three functions into a new viommu_api file, to build it with the > > IOMMUFD_DRIVER config. > > > > Signed-off-by: Nicolin Chen > > --- > > drivers/iommu/iommufd/Makefile | 2 +- > > drivers/iommu/iommufd/viommu_api.c | 39 ++++++++++++++++++++++++++++++ > > include/linux/iommufd.h | 16 ++++++++++++ > > 3 files changed, 56 insertions(+), 1 deletion(-) > > create mode 100644 drivers/iommu/iommufd/viommu_api.c > > I still think this is better to just share the struct content with the > driver, eventually we want to do this anyhow as the driver will > want to use container_of() techniques to reach its private data. In my mind, exposing everything to the driver is something that we have to (for driver-managed structures) v.s. we want to... Even in that case, a driver actually only need to know the size of the core structure, without touching what's inside(?). I am a bit worried that drivers would abuse the content in the core-level structure.. Providing a set of API would encourage them to keep the core structure intact, hopefully.. > > +/* > > + * Find a device attached to an VIOMMU object using a virtual device ID that was > > + * set via an IOMMUFD_CMD_VIOMMU_SET_VDEV_ID. Callers of this function must call > > + * iommufd_viommu_lock_vdev_id() prior and iommufd_viommu_unlock_vdev_id() after > > + * > > + * Return device or NULL. > > + */ > > +struct device *iommufd_viommu_find_device(struct iommufd_viommu *viommu, u64 id) > > +{ > > + struct iommufd_vdev_id *vdev_id; > > + > > + lockdep_assert_held(&viommu->vdev_ids_rwsem); > > + > > + xa_lock(&viommu->vdev_ids); > > + vdev_id = xa_load(&viommu->vdev_ids, (unsigned long)id); > > + xa_unlock(&viommu->vdev_ids); > > No need for this lock, xa_load is rcu safe against concurrent writer I see iommufd's device.c and main.c grab xa_lock before xa_load? Thanks Nicolin