Re: [PATCH] iommufd: Deal with IOMMU_HWPT_FAULT_ID_VALID in iommufd core

[Jason Gunthorpe <jgg@nvidia.com>]

On Sat, Dec 07, 2024 at 04:01:08AM -0800, Yi Liu wrote:
> IOMMU_HWPT_FAULT_ID_VALID is used to mark if the fault_id field of
> iommu_hwp_alloc is valid or not. As the fault_id field is handled in
> the iommufd core, so it makes sense to sanitize the
> IOMMU_HWPT_FAULT_ID_VALID flag in the iommufd core, and mask it out
> before passing the user flags to the iommu drivers.
> 
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c |  8 +-------
>  drivers/iommu/intel/iommu.c                         |  3 +--
>  drivers/iommu/iommufd/hw_pagetable.c                | 10 +++++++---
>  drivers/iommu/iommufd/selftest.c                    |  2 +-
>  4 files changed, 10 insertions(+), 13 deletions(-)

I'm going to take this, but there is still something missing - drivers
do not check domain->iopf_handler during attach and will happily
install these domains without any HW support for fault reporting.

Not sure this is so great.. I suggest adding a flag to the iommu_ops
'supports_fault_reporting', as just a global flag if the driver could
*possibly* support this. Core code will fail attach (and maybe alloc?)
if it is not set. If it is set driver must check domain->iopf_handler
during attach against HW capability.

Jason