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

[Tony Krowiak <akrowiak@linux.ibm.com>]

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@linux.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();
> 
> Just a little remark, I guess we want to report 0 if available and
> -ENXIO if not.

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

>