Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback

[Tony Krowiak]

On 06/11/2018 05:23 AM, Pierre Morel wrote:
> On 08/06/2018 23:59, Tony Krowiak wrote:
> > On 06/07/2018 01:15 PM, Pierre Morel wrote:
> > >
>
> ...snip...
>
> > > > > > Why maintain a list of kvm_ap_matrix structures if we don't have 
> > > > > > to; it is stored
> > > > > > with the mediated matrix device which is passed in to all of the 
> > > > > > vfio_ap driver
> > > > > > callbacks.
> > > > >
> > > > > Because using the vm_list which is a static in kvm makes you stick 
> > > > > inside the kvm code.
> >
> > I understand your point here, but even if we did maintain a list of 
> > kvm_ap_matrix structures,
> > we still need the kvm code to configure the guest's CRYCB and 
> > eventually ECA.28. There is
> > also code in kvm-ap.c that is called from KVM.
>
> The only code from kvm-ap which is called from KVM is temporary code
> waiting for Harald to offer the clean interface to AP instructions.
>
> > The idea behind kvm-ap.c is that all code
> > related to configuration of AP structures in KVM is in this one spot.
>
> This I understand, but the code can be in one spot inside VFIO_AP instead
> of inside KVM.
> Putting the code inside KVM induce dependencies between KVM and AP
> while the kvm/vfio interface allows to avoid this dependency.
>
>
> The purpose of VFIO_AP is to handle the CRYCB, all get/clear/set crycb 
> masks
> functions should be in VFIO AP.
>
> If we use wrappers in KVM, since the CRYCB is an a SIE extension,
> it is legitimate, the KVM interface to the CRYCB should only
> handle bitmaps and be unaware of the vfio_ap internal structures.
>
>
> Another concern, the kvm_ap_validate_queue_sharing() should not be
> inside KVM because it is a decision of current VFIO_AP driver
> to not share the queues between guest of level 2.
>
> The Z architecture does not allow to share AP queues between
> guests of level 1 but we could re-engineer the AP bus and the '
> VFIO AP to offer queue sharing for guest level 2.
>
> This would be a new VFIO_AP driver (and an AP bus extension).
> We should not have to change KVM for this.

Based on your, Halil's and Janosch's comments, I will make the changes.

> Regards,
>
> Pierre
>
>
> > >