Re: [Qemu-arm] [PATCH v2 02/14] target/arm/cpu: Ensure we can use the pmu with kvm

[Richard Henderson]

On 6/21/19 6:34 PM, Andrew Jones wrote:
> We first convert the pmu property from a static property to one with
> its own accessors. Then we use the set accessor to check if the PMU is
> supported when using KVM. Indeed a 32-bit KVM host does not support
> the PMU, so this check will catch an attempt to use it at property-set
> time.
> 
> Signed-off-by: Andrew Jones <address@hidden>
> ---
>  target/arm/cpu.c     | 30 +++++++++++++++++++++++++-----
>  target/arm/kvm.c     |  9 +++++++++
>  target/arm/kvm_arm.h | 13 +++++++++++++
>  3 files changed, 47 insertions(+), 5 deletions(-)
> 
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 376db154f008..858f668d226e 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -759,10 +759,6 @@ static Property arm_cpu_has_el3_property =
>  static Property arm_cpu_cfgend_property =
>              DEFINE_PROP_BOOL("cfgend", ARMCPU, cfgend, false);
>  
> -/* use property name "pmu" to match other archs and virt tools */
> -static Property arm_cpu_has_pmu_property =
> -            DEFINE_PROP_BOOL("pmu", ARMCPU, has_pmu, true);
> -
>  static Property arm_cpu_has_vfp_property =
>              DEFINE_PROP_BOOL("vfp", ARMCPU, has_vfp, true);
>  
> @@ -785,6 +781,29 @@ static Property arm_cpu_pmsav7_dregion_property =
>                                             pmsav7_dregion,
>                                             qdev_prop_uint32, uint32_t);
>  
> +static bool arm_get_pmu(Object *obj, Error **errp)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +
> +    return cpu->has_pmu;
> +}
> +
> +static void arm_set_pmu(Object *obj, bool value, Error **errp)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +
> +    if (value) {
> +        if (kvm_enabled() && !kvm_arm_pmu_supported(CPU(cpu))) {
> +            error_setg(errp, "'pmu' feature not supported by KVM on this 
> host");
> +            return;
> +        }
> +        set_feature(&cpu->env, ARM_FEATURE_PMU);
> +    } else {
> +        unset_feature(&cpu->env, ARM_FEATURE_PMU);
> +    }
> +    cpu->has_pmu = value;
> +}
> +
>  static void arm_get_init_svtor(Object *obj, Visitor *v, const char *name,
>                                 void *opaque, Error **errp)
>  {
> @@ -859,7 +878,8 @@ void arm_cpu_post_init(Object *obj)
>      }
>  
>      if (arm_feature(&cpu->env, ARM_FEATURE_PMU)) {
> -        qdev_property_add_static(DEVICE(obj), &arm_cpu_has_pmu_property,
> +        cpu->has_pmu = true;
> +        object_property_add_bool(obj, "pmu", arm_get_pmu, arm_set_pmu,
>                                   &error_abort);

This doesn't look right.

The static property is only enabled here if the cpu is known to support the
PMU, and thus the only useful setting is -cpu foo,pmu=off.  Which means that
the extra checking that you do in the dynamic property is unused.

It seems like you need to be checking for the PMU earlier, e.g. in
kvm_arm_get_host_cpu_features.


r~