Re: [RFC] iommu_ops->domain_alloc_paging() enhancement to support AMD IOMMU driver

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Jul 01, 2024 at 04:18:01PM +0530, Vasant Hegde wrote:

> > Then VFIO will just request the V2 domain anyhow and you are right
> > back to the starting problem again.
> 
> Let me see if I can put together here.
> 
> 
> - Basically we want domain_alloc_paging() to explicitly tell domain requirement
> (ex: allocate PASID capable UNMANAGED domain)
>   If we do that then we will fix ordering issue I described earlier.
> - Fix attach device path so that for 'PASID capable UNMANAGED domain' :
>   non-PASID capable device will use AMD V2 page table with GCR3[0]
>   PASID capable device will setup its GCR3 table as well and it should work fine.
> 
> Net we need a enhancement to domain_alloc_paging(). Otherwise I don't see a way
> to reliable implement things.

Yes, some flag at domain allocation time is clearly needed

But you need the whole story, including when will VFIO set the flag,
which requires a uAPI someplace.

> But these two can go independently?

If PASID goes with a default-on uAPI then you loose what you are
asking for as VFIO will always request PASID.

So the overall plan has to be sorted out now..

Jason