Re: [PATCH RFCv2] iommu: Add domain type and flag to domain_alloc_paging()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Aug 07, 2024 at 10:22:00PM +0530, Vasant Hegde wrote:
> > Needs more words, maybe even two flags?
> > 
> >  @IOMMU_HWPT_ALLOC_DEV_PASID: When the domain is used on a device,
> >  with no PASID, the device will support later attaching a PASID as
> >  well. Some HW requires a specific domain format on the device to
> >  allow PASID to work.
> 
> I will add this.
>
> >  @IOMMU_HWPT_ALLOC_PASID: The domain can be used as a PASID. The
> >  domain attached to the device must have also been allocated with
> >  IOMMU_HWPT_ALLOC_DEV_PASID.
> 
> Why do we need this flag? Previous one is already allocated PASID capable
> domain. Is this similar to SVA domain?

IOMMU_HWPT_ALLOC_DEV_PASID is the flag you specify to allocate the
domain you will attach to the RID

IOMMU_HWPT_ALLOC_PASID is the flag you specify if you intend to attach
this domain to a PASID

They are actually different operations from a user perspective. Today
every iommu driver implements them with the same logic..

So I thought perhaps they should be seperate, at least if we get some
really crazy HW down the road the uAPI will still work. uAPI is a bit
more tricky because you can't change it.

> @Baolu, Do we need to make any changes to intel driver?

I think Intel ignores this issue, they have nice HW and their RID can
use both of their supported domain formats in all cases.

Jason