Re: [PATCH v3 04/14] KVM: s390: device attribute to set AP interpretive execution

[Tony Krowiak]

On 03/15/2018 12:00 PM, Pierre Morel wrote:
> On 15/03/2018 16:23, Tony Krowiak wrote:
> > On 03/14/2018 05:57 PM, Halil Pasic wrote:
> > > On 03/14/2018 07:25 PM, Tony Krowiak wrote:
> > > > The VFIO AP device model exploits interpretive execution of AP
> > > > instructions (APIE) to provide guests passthrough access to AP
> > > > devices. This patch introduces a new device attribute in the
> > > > KVM_S390_VM_CRYPTO device attribute group to set APIE from
> > > > the VFIO AP device defined on the guest.
> > > >
> > > > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > [..]
> > >
> > > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > > > index a60c45b..bc46b67 100644
> > > > --- a/arch/s390/kvm/kvm-s390.c
> > > > +++ b/arch/s390/kvm/kvm-s390.c
> > > > @@ -815,6 +815,19 @@ static int kvm_s390_vm_set_crypto(struct kvm 
> > > > *kvm, struct kvm_device_attr *attr)
> > > > sizeof(kvm->arch.crypto.crycb->dea_wrapping_key_mask));
> > > >           VM_EVENT(kvm, 3, "%s", "DISABLE: DEA keywrapping support");
> > > >           break;
> > > > +    case KVM_S390_VM_CRYPTO_INTERPRET_AP:
> > > > +        if (attr->addr) {
> > > > +            if (!test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_AP))
> > > Unlock mutex before returning?
> > The mutex is unlocked prior to return at the end of the function.
> > > Maybe flip conditions (don't allow manipulating apie if feature not 
> > > there).
> > > Clearing the anyways clear apie if feature not there ain't too bad, but
> > > rejecting the operation appears nicer to me.
> > I think what you're saying is something like this:
> >
> >     if (!test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_AP))
> >         return -EOPNOTSUPP;
> >
> >     kvm->arch.crypto.apie = (attr->addr) ? 1 : 0;
> >
> > I can make arguments for doing this either way, but since the attribute
> > is will most likely only be set by an AP device in userspace, I suppose
> > it makes sense to allow setting of the attribute if the AP feature is
> > installed. It certainly makes sense for the dedicated implementation.
> > > > +                return -EOPNOTSUPP;
>
> Obviously Halil is speaking on this return statement.
> Which returns without unlocking the mutex.
Got it.
>