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

[Tony Krowiak]

On 05/24/2018 05:08 AM, Pierre Morel wrote:
> On 23/05/2018 16:45, Tony Krowiak wrote:
> > On 05/16/2018 04:03 AM, Pierre Morel wrote:
> > > On 07/05/2018 17:11, Tony Krowiak wrote:
> > > > Implements the open callback on the mediated matrix device.
> > > > The function registers a group notifier to receive notification
> > > > of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified,
> > > > the vfio_ap device driver will get access to the guest's
> > > > kvm structure. With access to this structure the driver will:
> > > >
> > > > 1. Ensure that only one mediated device is opened for the guest
>
> You should explain why.
>
> > > > 2. Configure access to the AP devices for the guest.
> ...snip...
> > > > +void kvm_ap_refcount_inc(struct kvm *kvm)
> > > > +{
> > > > +    atomic_inc(&kvm->arch.crypto.aprefs);
> > > > +}
> > > > +EXPORT_SYMBOL(kvm_ap_refcount_inc);
> > > > +
> > > > +void kvm_ap_refcount_dec(struct kvm *kvm)
> > > > +{
> > > > +    atomic_dec(&kvm->arch.crypto.aprefs);
> > > > +}
> > > > +EXPORT_SYMBOL(kvm_ap_refcount_dec);
> > >
> > > Why are these functions inside kvm-ap ?
> > > Will anyone use this outer of vfio-ap ?
> >
> > As I've stated before, I made the choice to contain all interfaces that
> > access KVM in kvm-ap because I don't think it is appropriate for the 
> > device
> > driver to have to have "knowledge" of the inner workings of KVM. Why 
> > does
> > it matter whether any entity outside of the vfio_ap device driver calls
> > these functions? I could ask a similar question if the interfaces were
> > contained in vfio-ap; what if another device driver needs access to 
> > these
> > interfaces?
>
> This is very driver specific and only used during initialization.
> It is not a common property of the cryptographic interface.
>
> I really think you should handle this inside the driver.

We are going to have to agree to disagree on this one. Is it not possible
that future drivers - e.g., when full virtualization is implemented - will
require access to KVM?
> Pierre
>
>
> ...snip...