Re: [PATCH 3/7] target/arm/cpu: spe: Add an option to turn on/off vSPE support

[Richard Henderson <richard.henderson@linaro.org>]

On 8/7/20 1:10 AM, Haibo Xu wrote:
> +static void arm_set_spe(Object *obj, bool value, Error **errp)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +
> +    if (value) {
> +        if (kvm_enabled() && !kvm_arm_spe_supported()) {
> +            error_setg(errp, "'spe' feature not supported by KVM on this host");
> +            return;
> +        }
> +        set_feature(&cpu->env, ARM_FEATURE_SPE);
> +    } else {
> +        unset_feature(&cpu->env, ARM_FEATURE_SPE);
> +    }
> +    cpu->has_spe = value;
> +}

I think you want to simply set cpu->has_spe here, and leave the adjustment of
ID_AA64DFR0 to a finalize routine.  Because there are multiple values that
PMSVer can take.

Once the get/set routines are only setting a flag on ARMCPU, you can use a
simpler property interface:

static Property arm_cpu_spe_property =
    DEFINE_PROP_BOOL("spe", ARMCPU, has_spe, true);

qdev_property_add_static(DEVICE(obj), &arm_cpu_spe_property);

The finalize routine would be called from arm_cpu_finalize_features(), much
like the existing arm_cpu_sve_finalize().

Since you're only registering the spe property when the selected cpu supports
spe, the finalize routine only needs to set PMSVer to 0 to turn it off,
preserving the initial enabled value of 1 or 2.


r~