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 nicolinc@nvidia.com
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