Re: [qemu-s390x] [PATCH v8 3/6] s390x/kvm: enable/disable AP instruction interpretation for guest

[David Hildenbrand]

Am 12.09.18 um 22:08 schrieb Tony Krowiak:
> From: Tony Krowiak <address@hidden>
> 
> Let's use the KVM_SET_DEVICE_ATTR ioctl to enable or disable
> hardware interpretation of AP instructions executed on the guest.
> If the S390_FEAT_AP feature is installed, AP instructions will
> be interpreted by default; otherwise, they will be intercepted.
> This attribute setting may be overridden by a device. For example,
> a device may want to provide AP instructions to the guest (i.e.,
> S390_FEAT_AP turned on), but it may want to emulate them. In this
> case, the AP instructions executed on the guest must be
> intercepted; so when the device is realized, it must disable
> interpretation.
> 
> Signed-off-by: Tony Krowiak <address@hidden>
> ---
>  target/s390x/kvm.c |   16 ++++++++++++++++
>  1 files changed, 16 insertions(+), 0 deletions(-)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index c4bd84d..28a3900 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -2297,6 +2297,19 @@ void kvm_s390_get_host_cpu_model(S390CPUModel *model, 
> Error **errp)
>                 S390_FEAT_MAX);
>  }
>  
> +static void kvm_s390_configure_apie(int interpret)
> +{
> +    uint64_t attr = KVM_S390_VM_CRYPTO_DISABLE_APIE;
> +
> +    if (interpret) {
> +        attr = KVM_S390_VM_CRYPTO_ENABLE_APIE;
> +    }
> +
> +    if (kvm_vm_check_attr(kvm_state, KVM_S390_VM_CRYPTO, attr)) {
> +            kvm_s390_set_attr(attr);
> +    }
> +}
> +
>  void kvm_s390_apply_cpu_model(const S390CPUModel *model, Error **errp)
>  {
>      struct kvm_s390_vm_cpu_processor prop  = {
> @@ -2346,6 +2359,9 @@ void kvm_s390_apply_cpu_model(const S390CPUModel 
> *model, Error **errp)
>      if (test_bit(S390_FEAT_CMM, model->features)) {
>          kvm_s390_enable_cmma();
>      }
> +
> +    /* configure hardware interpretation of AP instructions */
> +    kvm_s390_configure_apie(test_bit(S390_FEAT_AP, model->features));
>  }
>  

As it is off as default,

if (test_bit(S390_FEAT_AP, model->features)) {
        kvm_s390_configure_apie(true, model->features));
}

will save one ioctl without AP when starting a guest.


As mentioned as replay to patch #2, instead of KVM_S390_VM_CPU_FEAT_AP,
I think we can simply do the following in kvm_s390_get_host_cpu_model()


/* for now, we can only provide the AP feature with HW support */
if (kvm_vm_check_attr(kvm_state, KVM_S390_VM_CRYPTO,
    KVM_S390_VM_CRYPTO_ENABLE_APIE)) {
        set_bit(S390_FEAT_AP, model->features);
}


Apart from that, looks good to me.

-- 

Thanks,

David / dhildenb