Re: [PATCH v3 07/14] iommufd/viommu: Add iommufd_viommu_get_vdev_id helper

[Baolu Lu <baolu.lu@linux.intel.com>]

On 12/18/24 13:00, Nicolin Chen wrote:
> This is a reverse search v.s. iommufd_viommu_find_dev, as drivers may want
> to convert a struct device pointer (physical) to its virtual device ID for
> an event injection to the user space VM.
> 
> Again, this avoids exposing more core structures to the drivers, than the
> iommufd_viommu alone.
> 
> Signed-off-by: Nicolin Chen<nicolinc@nvidia.com>
> ---
>   include/linux/iommufd.h        |  8 ++++++++
>   drivers/iommu/iommufd/driver.c | 20 ++++++++++++++++++++
>   2 files changed, 28 insertions(+)
> 
> diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
> index b082676c9e43..ac1f1897d290 100644
> --- a/include/linux/iommufd.h
> +++ b/include/linux/iommufd.h
> @@ -190,6 +190,8 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
>   					     enum iommufd_object_type type);
>   struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
>   				       unsigned long vdev_id);
> +unsigned long iommufd_viommu_get_vdev_id(struct iommufd_viommu *viommu,
> +					 struct device *dev);

Hi Nicolin,

This series overall looks good to me. But I have a question that might
be irrelevant to this series itself.

The iommufd provides both IOMMUFD_OBJ_DEVICE and IOMMUFD_OBJ_VDEVICE
objects. What is the essential difference between these two from
userspace's perspective? And, which object ID should the IOMMU device
driver provide when reporting other events in the future?

Currently, the IOMMUFD uAPI reports IOMMUFD_OBJ_DEVICE in the page
fault message, and IOMMUFD_OBJ_VDEVICE (if I understand it correctly) in
the vIRQ message. It will be more future-proof if this could be defined
clearly.

Thanks,
baolu