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

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Aug 29, 2024 at 04:21:32PM +0530, Vasant Hegde wrote:
> >> Note that when we use NESTED page table it will have both v1 (L2 /
> >> stage 2 level) and v2 page table (L1 / stage 1 level). Even in this
> >> setup V2 page table inside guest can support PASID.
> >>
> > Sorry I am still confused. So V2 can support both PASID and no PASID
> > (untagged DMA). For the nested case, if the guest wants to allocate
> > a UNMANAGED domain, would you use V1? If this code in [3/5] below runs
> > in the guest:
> 
> In nested scenario, Guest will always use V2 page table (and host will use V1
> page table).

Sure, that is how it must work but..

> > static struct iommu_domain *amd_iommu_domain_alloc(unsigned int type)
> > 
> > 	/*
> > 	 * Force IOMMU v1 page table when allocating
> > 	 * domain for pass-through devices.
> > 	 */
> > 	if (type == IOMMU_DOMAIN_UNMANAGED)
> > 		pgtable = AMD_IOMMU_V1;
> > 
> > Hardware-wise, in nested case, can V1 be used in L1/S1 for DMA w/o
> > PASID?
> 
> Actually no. L1 (Guest) will use V2 page table. 

Where is the code for this? How does it work today?

I have the same confusion as Jacob where I don't see the driver making
the distinction - ie as above...

Jason