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

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Date:   Tue, 25 Sep 2018 09:24:57 -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 02:51 PM, 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@...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;
> 
> Did you mean to set vcpu->arch.sie_block->eca here?

Yes!

> 
>>
>>    	if (vcpu->kvm->arch.crypto.apie)
>>    		vcpu->arch.sie_block->eca |= ECA_APIE;
>>
> 
> Apart from that, just what I had in mind :)
>