Re: [RFC v2 4/5] target/arm: Enable feature ARM_FEATURE_EL2 if EL2 is supported

[Peter Maydell]

On Fri, 9 Feb 2024 at 16:00, Eric Auger <eric.auger@redhat.com> wrote:
>
> From: Haibo Xu <haibo.xu@linaro.org>
>
> KVM_CAP_ARM_EL2 must be supported by the cpu to enable ARM_FEATURE_EL2.
> In case the host does support NV, expose the feature.
>
> Signed-off-by: Haibo Xu <haibo.xu@linaro.org>
> Signed-off-by: Miguel Luis <miguel.luis@oracle.com>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> v1 -> v2:
> - remove isar_feature_aa64_aa32_el2 modif in target/arm/cpu.h
>   [Richard] and use el2_supported in kvm_arch_init_vcpu
> ---
>  target/arm/kvm.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 0996866afe..a08bc68a3f 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -238,6 +238,7 @@ static bool 
> kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>       */
>      int fdarray[3];
>      bool sve_supported;
> +    bool el2_supported;
>      bool pmu_supported = false;
>      uint64_t features = 0;
>      int err;
> @@ -268,6 +269,14 @@ static bool 
> kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>          init.features[0] |= 1 << KVM_ARM_VCPU_SVE;
>      }
>
> +    /*
> +     * Ask for EL2 if supported.
> +     */
> +    el2_supported = kvm_arm_el2_supported();
> +    if (el2_supported) {
> +        init.features[0] |= 1 << KVM_ARM_VCPU_HAS_EL2;
> +    }
> +
>      /*
>       * Ask for Pointer Authentication if supported, so that we get
>       * the unsanitized field values for AA64ISAR1_EL1.
> @@ -449,6 +458,10 @@ static bool 
> kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>      features |= 1ULL << ARM_FEATURE_PMU;
>      features |= 1ULL << ARM_FEATURE_GENERIC_TIMER;
>
> +    if (el2_supported) {
> +        features |= 1ULL << ARM_FEATURE_EL2;
> +    }
> +
>      ahcf->features = features;
>
>      return true;
> @@ -1912,6 +1925,9 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          cpu->kvm_init_features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
>                                        1 << KVM_ARM_VCPU_PTRAUTH_GENERIC);
>      }
> +    if (kvm_arm_el2_supported()) {
> +        cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_HAS_EL2;
> +    }
>
>      /* Do KVM_ARM_VCPU_INIT ioctl */
>      ret = kvm_arm_vcpu_init(cpu);

Am I reading this right that if the kernel supports FEAT_NV
then we will always ask for a vCPU with that feature?
Is that a good idea, or should we arrange to only do it if
the user uses the 'virtualization=on' option to -M virt ?
(Or does that happen already in some way I'm not seeing?)

thanks
-- PMM