Re: [PATCH v10 11/26] s390: vfio-ap: implement mediated device open callback

From: David Hildenbrand
Date: Mon Sep 24 2018 - 14:40:32 EST

On 24/09/2018 18:07, Tony Krowiak wrote:
> On 09/24/2018 04:40 AM, David Hildenbrand wrote:
>>> /**
>>> - * Verify that the AP instructions are available on the guest. This is
>>> indicated
>>> - * via the KVM_S390_VM_CPU_FEAT_AP CPU model feature.
>>> + * Verify that the AP instructions are being interpreted by firmware
>>> for the
>>> + * guest. This is indicated by the kvm->arch.crypto.apie flag.
>>> */
>>> static int kvm_ap_validate_crypto_setup(struct kvm *kvm)
>>> {
>>> - if (test_bit_inv(KVM_S390_VM_CPU_FEAT_AP, kvm->arch.cpu_feat))
>>> + if (kvm->arch.crypto.apie)
>>> return 0;
>> I wonder if this check makes sense, because apie can be toggled during
>> runtime. I guess it would be sufficient to check if the ap control block
>> is available and apie is supported by the HW.
> I am not clear about what you are getting at here, but I'll attempt
> to respond. There is no need to check if the AP control block (CRYCB)
> is available as the address is set in the CRYCBD three instructions
> above, even if AP instructions are not available. Regarding whether apie
> is supported by the hardware, the value of vcpu->kvm->arch.crypto.apie
> can not be set unless it is supported by the HW. In the patch (24/26)
> that provides the VM attributes to toggle this value, it can only be
> turned on if the AP instructions are available. I might also note that
> the kvm_ap_validate_crypto_setup() function is called whenever one of
> the VM crypto attributes is changed, so it makes sense that decisions
> made in this function are based on a change to a VM crypto attribute. In
> my first pass at changing this function, I checked
> ap_instructions_available() here, but after considering all of the
> above, it made sense to me to check the apie flag.

I prefer ap_instructions_available(). As I said, kvm->arch.crypto.apie
is a moving target.



David / dhildenb