Re: [PATCH v2 2/2] target/arm/kvm: add kvm-psci-version vcpu property

[Eric Auger <eric.auger@redhat.com>]

On 10/30/25 5:59 PM, Sebastian Ott wrote:
> Provide a kvm specific vcpu property to override the default
> (as of kernel v6.13 that would be PSCI v1.3) PSCI version emulated
> by kvm. Current valid values are: 0.1, 0.2, 1.0, 1.1, 1.2, and 1.3
>
> Signed-off-by: Sebastian Ott <sebott@redhat.com>
> ---
>  docs/system/arm/cpu-features.rst |  5 +++
>  target/arm/cpu.h                 |  6 ++++
>  target/arm/kvm.c                 | 60 +++++++++++++++++++++++++++++++-
>  3 files changed, 70 insertions(+), 1 deletion(-)
>
> diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst
> index 37d5dfd15b..1d32ce0fee 100644
> --- a/docs/system/arm/cpu-features.rst
> +++ b/docs/system/arm/cpu-features.rst
> @@ -204,6 +204,11 @@ the list of KVM VCPU features and their descriptions.
>    the guest scheduler behavior and/or be exposed to the guest
>    userspace.
>  
> +``kvm-psci-version``
> +  Override the default (as of kernel v6.13 that would be PSCI v1.3)
> +  PSCI version emulated by the kernel. Current valid values are:
> +  0.1, 0.2, 1.0, 1.1, 1.2, and 1.3
> +
>  TCG VCPU Features
>  =================
>  
> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> index 39f2b2e54d..c2032070b7 100644
> --- a/target/arm/cpu.h
> +++ b/target/arm/cpu.h
> @@ -981,6 +981,12 @@ struct ArchCPU {
>       */
>      uint32_t psci_version;
>  
> +    /*
> +     * Intermediate value used during property parsing.
> +     * Once finalized, the value should be read from psci_version.
> +     */
> +    uint32_t prop_psci_version;
> +
>      /* Current power state, access guarded by BQL */
>      ARMPSCIState power_state;
>  
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 0d57081e69..c53b307b76 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -484,6 +484,49 @@ static void kvm_steal_time_set(Object *obj, bool value, Error **errp)
>      ARM_CPU(obj)->kvm_steal_time = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
>  }
>  
> +struct psci_version {
> +    uint32_t number;
> +    const char *str;
> +};
> +
> +static const struct psci_version psci_versions[] = {
> +    { QEMU_PSCI_VERSION_0_1, "0.1" },
> +    { QEMU_PSCI_VERSION_0_2, "0.2" },
> +    { QEMU_PSCI_VERSION_1_0, "1.0" },
> +    { QEMU_PSCI_VERSION_1_1, "1.1" },
> +    { QEMU_PSCI_VERSION_1_2, "1.2" },
> +    { QEMU_PSCI_VERSION_1_3, "1.3" },
> +    { -1, NULL },
> +};
> +
> +static char *kvm_get_psci_version(Object *obj, Error **errp)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +    const struct psci_version *ver;
> +
> +    for (ver = psci_versions; ver->number != -1; ver++) {
> +        if (ver->number == cpu->prop_psci_version)
I still have the same question/comment as on v1. In case the end user
does not override the psci version I think you want to return the
default value, retrieved from KVM through KVM_REG_ARM_PSCI_VERSION and
which populates cpu->psci_version. So to me you should use
cpu->psci_version instead

> +            return g_strdup(ver->str);
> +    }
> +
> +    g_assert_not_reached();
> +}
> +
> +static void kvm_set_psci_version(Object *obj, const char *value, Error **errp)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +    const struct psci_version *ver;
> +
> +    for (ver = psci_versions; ver->number != -1; ver++) {
> +        if (!strcmp(value, ver->str)) {
> +            cpu->prop_psci_version = ver->number;
> +            return;
> +        }
> +    }
> +
> +    error_setg(errp, "Invalid PSCI-version value");
> +}
> +
>  /* KVM VCPU properties should be prefixed with "kvm-". */
>  void kvm_arm_add_vcpu_properties(ARMCPU *cpu)
>  {
> @@ -505,6 +548,12 @@ void kvm_arm_add_vcpu_properties(ARMCPU *cpu)
>                               kvm_steal_time_set);
>      object_property_set_description(obj, "kvm-steal-time",
>                                      "Set off to disable KVM steal time.");
> +
> +    object_property_add_str(obj, "kvm-psci-version", kvm_get_psci_version,
> +                            kvm_set_psci_version);
> +    object_property_set_description(obj, "kvm-psci-version",
> +                                    "Set PSCI version. "
> +                                    "Valid values are 0.1, 0.2, 1.0, 1.1, 1.2, 1.3");
>  }
>  
>  bool kvm_arm_pmu_supported(void)
> @@ -1959,7 +2008,8 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      if (cs->start_powered_off) {
>          cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_POWER_OFF;
>      }
> -    if (kvm_check_extension(cs->kvm_state, KVM_CAP_ARM_PSCI_0_2)) {
> +    if (cpu->prop_psci_version != QEMU_PSCI_VERSION_0_1 &&
I don't understand what this change stands for. Please document it
through both a comment and a commit msg explanation

Thanks

Eric
> +        kvm_check_extension(cs->kvm_state, KVM_CAP_ARM_PSCI_0_2)) {
>          cpu->psci_version = QEMU_PSCI_VERSION_0_2;
>          cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_PSCI_0_2;
>      }
> @@ -1998,6 +2048,14 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          }
>      }
>  
> +    if (cpu->prop_psci_version) {
> +        psciver = cpu->prop_psci_version;
> +        ret = kvm_set_one_reg(cs, KVM_REG_ARM_PSCI_VERSION, &psciver);
> +        if (ret) {
> +            error_report("PSCI version %"PRIx64" is not supported by KVM", psciver);
> +            return ret;
> +        }
> +    }
>      /*
>       * KVM reports the exact PSCI version it is implementing via a
>       * special sysreg. If it is present, use its contents to determine