Re: [PATCH v6 09/14] iommu/vt-d: Add IOMMU_HWPT_ALLOC_PASID support

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

On 12/19/24 21:27, Yi Liu wrote:
> Intel iommu driver just treats it as a nop since Intel VT-d does not have
> special requirement on domains attached to either the PASID or RID of a
> PASID-capable device.
> 
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>   drivers/iommu/intel/iommu.c  | 3 ++-
>   drivers/iommu/intel/nested.c | 2 +-
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index cd5e339fd5bb..0a622a89d876 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -3347,7 +3347,8 @@ intel_iommu_domain_alloc_paging_flags(struct device *dev, u32 flags,
>   	bool first_stage;
>   
>   	if (flags &
> -	    (~(IOMMU_HWPT_ALLOC_NEST_PARENT | IOMMU_HWPT_ALLOC_DIRTY_TRACKING)))
> +	    (~(IOMMU_HWPT_ALLOC_NEST_PARENT | IOMMU_HWPT_ALLOC_DIRTY_TRACKING |
> +	       IOMMU_HWPT_ALLOC_PASID)))
>   		return ERR_PTR(-EOPNOTSUPP);
>   	if (nested_parent && !nested_supported(iommu))
>   		return ERR_PTR(-EOPNOTSUPP);
> diff --git a/drivers/iommu/intel/nested.c b/drivers/iommu/intel/nested.c
> index aba92c00b427..6ac5c534bef4 100644
> --- a/drivers/iommu/intel/nested.c
> +++ b/drivers/iommu/intel/nested.c
> @@ -198,7 +198,7 @@ intel_iommu_domain_alloc_nested(struct device *dev, struct iommu_domain *parent,
>   	struct dmar_domain *domain;
>   	int ret;
>   
> -	if (!nested_supported(iommu) || flags)
> +	if (!nested_supported(iommu) || flags & ~IOMMU_HWPT_ALLOC_PASID)
>   		return ERR_PTR(-EOPNOTSUPP);
>   
>   	/* Must be nested domain */

It's better to abort and fail a domain allocation when
IOMMU_HWPT_ALLOC_PASID is set but the iommu lacks pasid support?

Another related consideration is the support for page faults in nested
domains once PASID is available in user space. Would it be reasonable to
support page faults for nested domains?

If so, perhaps it's time to open intel_iommu_domain_alloc_nested() to
support IOMMU_HWPT_FAULT_ID_VALID when PRI is enabled on the device?

--
baolu