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

[Pierre Morel]

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)
> > > +{
> > > +ÂÂÂ atomic_inc(&kvm->arch.crypto.aprefs);
> > > +}
> > > +EXPORT_SYMBOL(kvm_ap_refcount_inc);
> > > +
> > > +void kvm_ap_refcount_dec(struct kvm *kvm)
> > > +{
> > > +ÂÂÂ 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.

Pierre


...snip...


--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany