Re: [PATCH v8 4/5] iommufd: Extend IOMMU_GET_HW_INFO to report PASID capability

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Mar 13, 2025 at 05:47:52AM -0700, Yi Liu wrote:
> PASID usage requires PASID support in both device and IOMMU. Since the
> iommu drivers always enable the PASID capability for the device if it
> is supported, this extends the IOMMU_GET_HW_INFO to report the PASID
> capability to userspace. Also, enhances the selftest accordingly.

Overall, I am a bit confused by the out_capabilities field in the
IOMMU_GET_HW_INFO. Why these capabilities cannot be reported via
the driver specific data structure?

E.g. we don't report the "NESTING" capability in out_capabilities
at all and that works fine since the iommu driver would reject if
it doesn't support.

Mind elaborate the reason for these two new capabilities? What is
the benefit from keeping them in the core v.s. driver level?

(sorry for doubting this at such a late stage...)

> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org> #aarch64 platform
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>  drivers/iommu/iommufd/device.c | 35 +++++++++++++++++++++++++++++++++-
>  drivers/pci/ats.c              | 33 ++++++++++++++++++++++++++++++++
>  include/linux/pci-ats.h        |  3 +++
>  include/uapi/linux/iommufd.h   | 14 +++++++++++++-
>  4 files changed, 83 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index 70da39f5e227..1f3bec61bcf9 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -3,6 +3,8 @@
>   */
>  #include <linux/iommu.h>
>  #include <linux/iommufd.h>
> +#include <linux/pci.h>
> +#include <linux/pci-ats.h>

"pci-ats" includes "pci.h" already.

Thanks
Nicolin