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

David Hildenbrand
2018-09-24T18:51:46Z

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();
> 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?

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

Apart from that, just what I had in mind :)

--

Thanks,

David / dhildenb