Re: [PATCH 1/5] iommu: Enhance domain allocation code to take additional flags

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Aug 22, 2024 at 07:27:39PM +0800, Yi Liu wrote:
> On 2024/8/22 00:31, Jason Gunthorpe wrote:
> 
> > > @@ -359,11 +359,17 @@ struct iommu_vfio_ioas {
> > >    *                                   enforced on device attachment
> > >    * @IOMMU_HWPT_FAULT_ID_VALID: The fault_id field of hwpt allocation data is
> > >    *                             valid.
> > > + * @IOMMUFD_HWPT_ALLOC_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.
> > 
> > Maybe:
> > 
> >   Requests a domain that can be used with PASID. The domain can be
> >   attached to any PASID on the device. Any domain attached to the
> >   non-PASID part of the device must also be flaged, otherwise attaching
> >   a PASID will blocked.
> > 
> > Yi will need to add a check that IOMMUFD_HWPT_ALLOC_PASID was
> > specified on the RID domain while processing attach on the PASID
> > domain.
> 
> this means if userspace wants to user pasid on a device, it should allocate
> hwpt with this flag, no matter the hwpt is going to be attached to RID or
> pasid. is it?

Yes

> I still have a confusion. Say on AMD, is it a legitimate configuration that
> the RID is attached to a domain that uses V1 page table while pasid is
> attached to domains that use V2 page table? From architecture p.o.v., it
> seems allowed.

I think that is exactly what they have been saying their design cannot
do.

If you want to use PASID you must install a GCR3 table full of V2
tables. Doing this denies use of the V1 format for anything except a
NESTING_PARENT.

Jason