Re: [PATCH RFC v1 02/15] iommu: Add a simple PASID table library

[Jean-Philippe Brucker]

On Fri, Mar 12, 2021 at 06:17:55PM +0530, Vivek Kumar Gautam wrote:
> > Regarding the overall design, I was initially assigning page directories
> > instead of whole PASID tables, which would simplify the driver and host
> > implementation. A major complication, however, is SMMUv3 accesses PASID
> > tables using a guest-physical address, so there is a messy negotiation
> > needed between host and guest when the host needs to allocate PASID
> > tables. Plus vSMMU needs PASID table assignment, so that's what the host
> > driver will implement.
> 
> By assigning the page directories, you mean setting up just the stage-1 page
> table ops, and passing that information to the host using ATTACH_TABLE?

Yes. And we can support nested translation with SMMUv2 that way. But with
SMMUv3 the guest has to manage the whole PASID table.

> Right now when using kvmtool, the struct iommu_pasid_table_config is
> populated with the correct information, and this whole memory is mapped
> between host and guest by creating a mem bank using
> kvm__for_each_mem_bank().
> Did I get you or did I fail terribly in understanding the point you are
> making here?

Makes sense

Thanks,
Jean