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

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Date:   Mon, 24 Sep 2018 14:42:48 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, pmorel@...ux.vnet.ibm.com,
        alifm@...ux.vnet.ibm.com, mjrosato@...ux.vnet.ibm.com,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com,
        frankja@...ux.ibm.com
Subject: Re: [PATCH v10 24/26] KVM: s390: device attrs to enable/disable AP
 interpretation

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@...ux.ibm.com>
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();
  			break;
  		default:
  			ret = -ENXIO;
@@ -2620,6 +2626,7 @@ static void kvm_s390_vcpu_crypto_setup(struct 
kvm_vcpu *vcpu)

  	vcpu->arch.sie_block->crycbd = vcpu->kvm->arch.crypto.crycbd;
  	vcpu->arch.sie_block->ecb3 &= ~(ECB3_AES | ECB3_DEA);
+	vcpu->kvm->arch.crypto.apie &= ~ECA_APIE;

  	if (vcpu->kvm->arch.crypto.apie)
  		vcpu->arch.sie_block->eca |= ECA_APIE;
-- 
2.19.0.221.g150f307

>>
>