Re: [PATCH v10 11/26] s390: vfio-ap: implement mediated device open callback

[Tony Krowiak]

On 09/24/2018 02:40 PM, David Hildenbrand wrote:
> On 24/09/2018 18:07, Tony Krowiak wrote:
> > On 09/24/2018 04:40 AM, David Hildenbrand wrote:
> > > >     /**
> > > > - * Verify that the AP instructions are available on the guest. This is
> > > > indicated
> > > > - * via the  KVM_S390_VM_CPU_FEAT_AP CPU model feature.
> > > > + * Verify that the AP instructions are being interpreted by firmware
> > > > for the
> > > > + * guest. This is indicated by the kvm->arch.crypto.apie flag.
> > > >      */
> > > >     static int kvm_ap_validate_crypto_setup(struct kvm *kvm)
> > > >     {
> > > > -	if (test_bit_inv(KVM_S390_VM_CPU_FEAT_AP, kvm->arch.cpu_feat))
> > > > +	if (kvm->arch.crypto.apie)
> > > >     		return 0;
> > >
> > > I wonder if this check makes sense, because apie can be toggled during
> > > runtime. I guess it would be sufficient to check if the ap control block
> > > is available and apie is supported by the HW.
> >
> > I am not clear about what you are getting at here, but I'll attempt
> > to respond. There is no need to check if the AP control block (CRYCB)
> > is available as the address is set in the CRYCBD three instructions
> > above, even if AP instructions are not available. Regarding whether apie
> > is supported by the hardware, the value of vcpu->kvm->arch.crypto.apie
> > can not be set unless it is supported by the HW. In the patch (24/26)
> > that provides the VM attributes to toggle this value, it can only be
> > turned on if the AP instructions are available. I might also note that
> > the kvm_ap_validate_crypto_setup() function is called whenever one of
> > the VM crypto attributes is changed, so it makes sense that decisions
> > made in this function are based on a change to a VM crypto attribute. In
> > my first pass at changing this function, I checked
> > ap_instructions_available() here, but after considering all of the
> > above, it made sense to me to check the apie flag.
>
> I prefer ap_instructions_available(). As I said, kvm->arch.crypto.apie
> is a moving target.

Okay then.

>