Re: [RFC PATCH v6 05/11] iommu: Add a helper to validate a vIOMMU parent

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Sep 28, 2026 at 11:08:54AM -0700, Jacob Pan wrote:
> Hi Jason,
> 
> On Mon, 28 Sep 2026 13:17:38 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> > On Mon, Sep 28, 2026 at 09:09:06PM +0530, Aneesh Kumar K.V wrote:
> > 
> > > Does that mean the SMMU driver will return viommu_ops before
> > > iommu_ops->viommu_init() is called? If so, should viommu_init() be
> > > moved into viommu_ops?  
> > 
> > That's probably the cleanest arrangement, yeah. Then the TSM ops are
> > just the same 'get_viommu_ops' call under TSM and it is easy to put in
> > a flag 'must have null hwpt' that goes at the right point.
> > 
> This should also work for the parentless hypervisor vIOMMU in my RFC:
> https://lore.kernel.org/linux-iommu/20260925190742.1575380-1-jacob.pan@linux.microsoft.com/T/#t

Yes! That case is very similar, the hypervisor under Linux is a close
cousin to RMM/TDX.

> I will give below a try, I currently have below (can be avoided if
> get_viommu_ops() can simply return NULL for the hypervisor type):

The amd_iommufd_get_viommu_ops() must only permit its own type, but
AMD doesn't have a type right now because they are merging their
patches bit by bit..

ARM already returns NULL:

> > +const struct iommufd_viommu_ops *
> > +arm_smmu_get_viommu_ops(struct device *dev, enum iommu_viommu_type
> > viommu_type) {
> >  	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> >  	struct arm_smmu_device *smmu = master->smmu;
> >  
> >  	if (!(smmu->features & ARM_SMMU_FEAT_NESTING))
> > +		return NULL;

Though I wonder why would you check for IOMMU_VIOMMU_TYPE_HYPERVISOR
in the amd driver?

Maybe hyperv should be a TSM?  Maybe we should also route the
get_viommu through the the "kvm" fd somehow?

Jason