Re: [RFC PATCH 05/12] s390/cio: add protected virtualization support to cio

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 10 Apr 2019 02:10:44 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Tue, 9 Apr 2019 19:55:48 +0200
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
> > On Fri,  5 Apr 2019 01:16:15 +0200
> > Halil Pasic <pasic@linux.ibm.com> wrote:

> > > Thus we need to make sure any memory that is used for communication with
> > > the hypervisor is shared.  
> > 
> > In this context, does 'hypervisor' always mean 'QEMU/KVM'? If Other
> > Hypervisors implement protected virtualization, we probably need to
> > make sure that all common I/O layer control blocks are in the dma area
> > (including e.g. QDIO), not just what virtio-ccw devices use.
> >   
> 
> Hypervisor could theoretically be something different than QEMU/KVM. Yet,
> as stated before, this series is about getting virtio-ccw working
> (modulo the TODOs). 

Sure, just wanted to point it out. If this is "enable the common I/O
layer, except for QDIO" or so, that would sound fine to me :)

> 
> [..]
> 
> > >    
> > 
> > So, this leaves some things I'm not sure about, especially as I do not
> > know the architecture of this new feature.
> > 
> > - This applies only to asynchronously handled things, it seems? So
> >   things like control blocks modified by stsch/msch/etc does not need
> >   special treatment?  
> 
> I had a feeble attempt at explaining this in the cover letter:
> 
> * make sure that virtio-ccw specific stuff uses shared memory when
>   talking to the hypervisor (except communication blocks like ORB, these
>   are handled by the hypervisor)
> 
> Unfortunately the last 'hypervisor' was supposed to be 'ultravisor'.
> 
> I.e. the ultravisor will take care of exposing the control blocks
> to the hypervisor (and of changes as well).

Yeah, that "control blocks" or "communication blocks" leaves me a bit
fuzzy :)

So, what is a high-level summary of areas that need the treatment?
What I get from looking at the patches so far, it's:
- stuff that is written by the hypervisor's interrupt injection code:
  IRB, indicators, etc.
- buffers that are filled by a channel program: sense, sense id, etc.
- ccws themselves (because of translation?)