Re: [Qemu-devel] [PATCH v3] s390x/cpumodel: Set up CPU model for AQIC interception

[Pierre Morel <pmorel@linux.ibm.com>]

On 14/02/2019 13:14, Pierre Morel wrote:
> A new CPU model facilities is introduced to support AP devices
> interruption interception for a KVM guest.
> 
> "APQI" for "AP-Queue Interruption" facility
> 
> The S390_FEAT_AP_QUEUE_INTERRUPT_CONTROL, CPU facility indicates
> whether the PQAP instruction with the AQIC command is available
> to the guest.
> This feature will be enabled only if the AP instructions are
> available on the linux host and AQIC facility is installed on
> the host.
> 
> This feature must be turned on from userspace to intercept AP
> instructions on the KVM guest. The QEMU command line to turn
> this feature on looks something like this:
> 
>      qemu-system-s390x ... -cpu xxx,apqi=on ...



Hi,

I suddenly have a very big doubt on this QEMU patch.

Older Linux advertise PQAP/AQIC feature (65)
Older Qemu mask it for the guest

Now if we set aqic = on in the new QEMU,
QEMU advertises feature (65)

The guest gets an OPERATION EXCEPTION even we advertised the feature 65.

This seems wrong to me, we should verify that the vfio_driver is loaded 
in the host before starting the guest with something like:

kvm_vm_check_attr(kvm_state, KVM_S390_VM_ENABLE_AQIC)

Don't you think?

Regards,

Pierre



> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
> ---
>   target/s390x/cpu_features.c     | 1 +
>   target/s390x/cpu_features_def.h | 1 +
>   target/s390x/cpu_models.c       | 1 +
>   target/s390x/gen-features.c     | 1 +
>   4 files changed, 4 insertions(+)
> 
> diff --git a/target/s390x/cpu_features.c b/target/s390x/cpu_features.c
> index 60cfeba..99bd382 100644
> --- a/target/s390x/cpu_features.c
> +++ b/target/s390x/cpu_features.c
> @@ -84,6 +84,7 @@ static const S390FeatDef s390_features[] = {
>       FEAT_INIT("sema", S390_FEAT_TYPE_STFL, 59, "Semaphore-assist facility"),
>       FEAT_INIT("tsi", S390_FEAT_TYPE_STFL, 60, "Time-slice Instrumentation facility"),
>       FEAT_INIT("ri", S390_FEAT_TYPE_STFL, 64, "CPU runtime-instrumentation facility"),
> +    FEAT_INIT("apqi", S390_FEAT_TYPE_STFL, 65, "AP-Queue interruption facility"),
>       FEAT_INIT("zpci", S390_FEAT_TYPE_STFL, 69, "z/PCI facility"),
>       FEAT_INIT("aen", S390_FEAT_TYPE_STFL, 71, "General-purpose-adapter-event-notification facility"),
>       FEAT_INIT("ais", S390_FEAT_TYPE_STFL, 72, "General-purpose-adapter-interruption-suppression facility"),
> diff --git a/target/s390x/cpu_features_def.h b/target/s390x/cpu_features_def.h
> index 5fc7e7b..3f22780 100644
> --- a/target/s390x/cpu_features_def.h
> +++ b/target/s390x/cpu_features_def.h
> @@ -72,6 +72,7 @@ typedef enum {
>       S390_FEAT_SEMAPHORE_ASSIST,
>       S390_FEAT_TIME_SLICE_INSTRUMENTATION,
>       S390_FEAT_RUNTIME_INSTRUMENTATION,
> +    S390_FEAT_AP_QUEUE_INTERRUPT_CONTROL,
>       S390_FEAT_ZPCI,
>       S390_FEAT_ADAPTER_EVENT_NOTIFICATION,
>       S390_FEAT_ADAPTER_INT_SUPPRESSION,
> diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c
> index 7c253ff..6b5e94b 100644
> --- a/target/s390x/cpu_models.c
> +++ b/target/s390x/cpu_models.c
> @@ -788,6 +788,7 @@ static void check_consistency(const S390CPUModel *model)
>           { S390_FEAT_SIE_KSS, S390_FEAT_SIE_F2 },
>           { S390_FEAT_AP_QUERY_CONFIG_INFO, S390_FEAT_AP },
>           { S390_FEAT_AP_FACILITIES_TEST, S390_FEAT_AP },
> +        { S390_FEAT_AP_QUEUE_INTERRUPT_CONTROL, S390_FEAT_AP },
>       };
>       int i;
> 
> diff --git a/target/s390x/gen-features.c b/target/s390x/gen-features.c
> index 70015ea..b051221 100644
> --- a/target/s390x/gen-features.c
> +++ b/target/s390x/gen-features.c
> @@ -448,6 +448,7 @@ static uint16_t full_GEN12_GA1[] = {
>       S390_FEAT_EDAT_2,
>       S390_FEAT_SIDE_EFFECT_ACCESS_ESOP2,
>       S390_FEAT_AP_QUERY_CONFIG_INFO,
> +    S390_FEAT_AP_QUEUE_INTERRUPT_CONTROL,
>       S390_FEAT_AP_FACILITIES_TEST,
>       S390_FEAT_AP,
>   };
> 


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany