Re: [PATCH 37/71] target/arm: Add cpu properties for SME

[Peter Maydell]

On Thu, 2 Jun 2022 at 23:33, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Mirror the properties for SVE.  The main difference is
> that any arbitrary set of powers of 2 may be supported,
> and not the stricter constraints that apply to SVE.
>
> Include a property to control FEAT_SME_FA64, as failing
> to restrict the runtime to the proper subset of insns
> could be a major point for bugs.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

> @@ -589,10 +589,13 @@ static void cpu_arm_get_vq(Object *obj, Visitor *v, 
> const char *name,
>      ARMCPU *cpu = ARM_CPU(obj);
>      ARMVQMap *vq_map = opaque;
>      uint32_t vq = atoi(&name[3]) / 128;
> +    bool sve = vq_map == &cpu->sve_vq;
>      bool value;
>
> -    /* All vector lengths are disabled when SVE is off. */
> -    if (!cpu_isar_feature(aa64_sve, cpu)) {
> +    /* All vector lengths are disabled when feature is off. */
> +    if (sve
> +        ? !cpu_isar_feature(aa64_sve, cpu)
> +        : !cpu_isar_feature(aa64_sme, cpu)) {
>          value = false;
>      } else {
>          value = extract32(vq_map->map, vq - 1, 1);

I was wondering what you were going to do about this bit; the
comparison against &cpu->sve_vq feels a bit awkward but I guess
it's the simplest thing.

> +void arm_cpu_sme_finalize(ARMCPU *cpu, Error **errp)
> +{
> +    uint32_t vq_map = cpu->sme_vq.map;
> +    uint32_t vq_init = cpu->sme_vq.init;
> +    uint32_t vq_supported = cpu->sme_vq.supported;
> +    uint32_t vq;
> +
> +    if (vq_map == 0) {
> +        if (!cpu_isar_feature(aa64_sme, cpu)) {
> +            cpu->isar.id_aa64smfr0 = 0;
> +            return;
> +        }
> +
> +        /* TODO: KVM will require limitations via SMCR_EL2. */
> +        vq_map = vq_supported & ~vq_init;

Do we currently forbid setting these properties entirely for KVM
(or just not provide them) ?

> +static void aarch64_add_sme_properties(Object *obj)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +    uint32_t vq;
> +
> +    object_property_add_bool(obj, "sme", cpu_arm_get_sme, cpu_arm_set_sme);
> +    object_property_add_bool(obj, "sme_fa64", cpu_arm_get_sme_fa64,
> +                             cpu_arm_set_sme_fa64);
> +
> +    for (vq = 1; vq <= ARM_MAX_VQ; vq <<= 1) {
> +        char name[8];
> +        sprintf(name, "sme%d", vq * 128);
> +        object_property_add(obj, name, "bool", cpu_arm_get_vq,
> +                            cpu_arm_set_vq, NULL, &cpu->sme_vq);
> +    }
> +
> +#ifdef CONFIG_USER_ONLY
> +    /* Mirror linux /proc/sys/abi/sme_default_vector_length. */
> +    object_property_add(obj, "sme-default-vector-length", "int32",
> +                        cpu_arm_get_default_vec_len,
> +                        cpu_arm_set_default_vec_len, NULL,
> +                        &cpu->sme_default_vq);
> +#endif
> +}

These new properties should be documented in
docs/system/arm/cpu-features.rst, similar to the SVE ones.

thanks
-- PMM