Re: [PATCH v10 24/26] KVM: s390: device attrs to enable/disable AP interpretation

[Tony Krowiak]

On 09/25/2018 03:32 AM, David Hildenbrand wrote:
> On 24/09/2018 20:42, Tony Krowiak wrote:
> > On 09/24/2018 12:25 PM, Tony Krowiak wrote:
> > > On 09/24/2018 07:23 AM, David Hildenbrand wrote:
> >
> > (...)
> >
> > > > Will you also fixup this patch to expose KVM_S390_VM_CRYPTO_ENABLE_APIE
> > > > only if supported by HW? (ap_instructions_available)
> > >
> > > Given that this patch DOES expose KVM_S390_VM_CRYPTO_ENABLE_APIE only if
> > > supported by HW, I assume you are talking about
> > > KVM_S390_VM_CRYPTO_DISABLE_APIE. I didn't check
> > > ap_instructions_available() for disabling APIE because I didn't
> > > think it necessary given that ECA.28 will be set to 0 (intercept) by
> > > default, whether AP instructions are installed or not; so why not allow
> > > disabling apie. I suppose from the perspective of consistency, since the
> > > kvm_s390_vm_has_attr() function checks ap_instructions_available() for
> > > both attributes, then it probably makes sense to add that check to
> > > KVM_S390_VM_CRYPTO_DISABLE_APIE here. Then again, we could make a change
> > > in ap_instructions_available() to allow KVM_S390_VM_CRYPTO_DISABLE_APIE
> > > regardless of whether AP instructions are available. It boils down to
> > > whether APIE needs to be dynamically disabled at some point when it has
> > > been enabled. The only case I can think of where that may be necessary
> > > is if a guest is migrated to a system without AP instructions. I don't
> > > think that can happen and may even be protected against precisely
> > > because the VM attributes won't be available on the target system due to
> > > no AP instructions. What say you?
> > David,
> >
> > I'm sorry, I misinterpreted what you were asking for. Check out the
> > fixup! patch below and let me know if that is what you are looking for.
> > If so, I will integrate that change and post v11 tomorrow (Tuesday 9/24).
> >
> > -----------------------------------8<-----------------------------------
> >
> > From: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > Date: Mon, 24 Sep 2018 14:18:37 -0400
> > Subject: [FIXUP v10] fixup! KVM: s390: device attrs to enable/disable AP
> >    interpretation
> >
> > ---
> >    arch/s390/kvm/kvm-s390.c | 9 ++++++++-
> >    1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index 6654bb1fc26a..a528558baa78 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -901,6 +901,10 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm,
> > struct kvm_device_attr *attr)
> >    		kvm->arch.crypto.apie = 1;
> >    		break;
> >    	case KVM_S390_VM_CRYPTO_DISABLE_APIE:
> > +		if (!ap_instructions_available()) {
> > +			mutex_unlock(&kvm->lock);
> > +			return -EOPNOTSUPP;
> > +		}
> >    		kvm->arch.crypto.apie = 0;
> >    		break;
> >    	default:
> > @@ -1509,9 +1513,11 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm,
> > struct kvm_device_attr *attr)
> >    		case KVM_S390_VM_CRYPTO_ENABLE_DEA_KW:
> >    		case KVM_S390_VM_CRYPTO_DISABLE_AES_KW:
> >    		case KVM_S390_VM_CRYPTO_DISABLE_DEA_KW:
> > +			ret = 0;
> > +			break;
> >    		case KVM_S390_VM_CRYPTO_ENABLE_APIE:
> >    		case KVM_S390_VM_CRYPTO_DISABLE_APIE:
> > -			ret = 0;
> > +			ret = ap_instructions_available();
>
> Just a little remark, I guess we want to report 0 if available and
> -ENXIO if not.

That makes sense ... I'll fix it.

>