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

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Message-ID: <62f0cacc-8338-9370-a4dc-12f793214c48@redhat.com>
Date:   Tue, 25 Sep 2018 09:32:26 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.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 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();

Just a little remark, I guess we want to report 0 if available and
-ENXIO if not.

-- 

Thanks,

David / dhildenb