Re: [PATCH 2/6] iommu/vt-d: Implement hw_info for iommu capability query

[Alex Williamson <alex.williamson@redhat.com>]

On Wed,  8 Feb 2023 20:16:38 -0800
Yi Liu <yi.l.liu@intel.com> wrote:

> From: Lu Baolu <baolu.lu@linux.intel.com>
> 
> To support nested translation in the userspace, it should check the
> underlying hardware information for the capabilities.
> 
> Add intel_iommu_hw_info() to report cap_reg and ecap_reg information.
> 
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c  | 19 +++++++++++++++++++
>  drivers/iommu/intel/iommu.h  |  1 +
>  include/uapi/linux/iommufd.h | 21 +++++++++++++++++++++
>  3 files changed, 41 insertions(+)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 59df7e42fd53..929f600cc350 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4760,8 +4760,26 @@ static void intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
>  	intel_pasid_tear_down_entry(iommu, dev, pasid, false);
>  }
>  
> +static void *intel_iommu_hw_info(struct device *dev, u32 *length)
> +{
> +	struct device_domain_info *info = dev_iommu_priv_get(dev);
> +	struct intel_iommu *iommu = info->iommu;
> +	struct iommu_device_info_vtd *vtd;
> +
> +	vtd = kzalloc(sizeof(*vtd), GFP_KERNEL);
> +	if (!vtd)
> +		return ERR_PTR(-ENOMEM);
> +
> +	vtd->cap_reg = iommu->cap;
> +	vtd->ecap_reg = iommu->ecap;

Just a friendly reminder that these registers are already exposed to
userspace under /sys/class/iommu/ and each device has an iommu link
back to their iommu device there.  This series doesn't really stand on
its own without some discussion of why that interface is not sufficient
for this use case.  Thanks,

Alex