Re: S390 testing for IOMMUFD

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Nov 08, 2022 at 08:50:53AM -0500, Matthew Rosato wrote:

> FWIW, vfio-pci via s390 is working fine so far, though I'll put it
> through more paces over the next few weeks and report if I find
> anything.

OK great

> As far as mdev drivers...  
> 
> -ccw: Sounds like Eric is already aware there is an issue and is investigating (I see errors as well).
> 
> -ap: I see the exact same issue that Christian mentioned...  I'll talk to Tony & Jason about it.

A clue what is going wrong might get a quick realization on the
problem?

I'm guessing something in the vfio side more than the access 'pinning'
part?

> > If I recall there was some desire from the S390 platform team to start
> > building on iommufd to create some vIOMMU acceleration for S390
> > guests, this is a necessary first step.
> 
> There's probably something here for -ccw in the future, but you
> might be thinking of s390 vfio-pci e.g. to implement the in-kernel
> handling of nested mappings on s390 -- yep, work in in progress
> here, not ready for sharing yet but I have been most recently basing
> my work on top of the nesting series
> https://github.com/yiliu1765/iommufd/tree/iommufd-v6.0-rc3-nesting

The relation is that if vfio-pci wants to do the above then
vfio-ccw/ap will have to run on iommufd when used in the same VM as
vfio-pci.

So we need it to work :)

Jason