Re: [Qemu-devel] [PATCH v13 4/5] i386: Verify and enable topoext feature if supported

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Jun 08, 2018 at 06:56:20PM -0400, Babu Moger wrote:
> If the CPU model supports topoext feature, enabled the
> feature automatically if it can be supported.
> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
>  target/i386/cpu.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 4dd9a82..88bc73d 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -4763,6 +4763,33 @@ static int x86_cpu_filter_features(X86CPU *cpu)
>  #define IS_AMD_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_AMD_1 && \
>                           (env)->cpuid_vendor2 == CPUID_VENDOR_AMD_2 && \
>                           (env)->cpuid_vendor3 == CPUID_VENDOR_AMD_3)
> +/*
> + * Check if we can support this topology
> + * Fail if number of cores are beyond the supported config
> + * or nr_threads is more than 2
> + */
> +static int topology_supports_topoext(int nr_cores, int nr_threads,
> +            Error **errp)
> +{
> +    if (nr_cores > (MAX_CORES_IN_NODE * MAX_NODES_PER_SOCKET)) {
> +        error_setg(errp, "TOPOEXT unsupported with %d cores per socket",
> +                   nr_cores);
> +        error_append_hint(errp, "TOPOEXT supports only up to %d cores per"
> +                          " socket\n",
> +                          (MAX_CORES_IN_NODE * MAX_NODES_PER_SOCKET));
> +        return false;
> +    }
> +
> +    if (nr_threads > 2) {
> +        error_setg(errp, "TOPOEXT unsupported with %d threads per core",
> +                   nr_threads);
> +        error_append_hint(errp, "TOPOEXT supports only up to 2 threads"
> +                          " per core\n");
> +        return false;
> +    }
> +    return true;
> +}
> +
>  static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
>  {
>      CPUState *cs = CPU(dev);
> @@ -4953,6 +4980,19 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
>  
>      qemu_init_vcpu(cs);
>  
> +    if (cpu->auto_topoext &&
> +        !(env->user_features[FEAT_8000_0001_ECX] & CPUID_EXT3_TOPOEXT)) {
> +        if (cs->nr_cores <= (MAX_CORES_IN_NODE * MAX_NODES_PER_SOCKET) &&
> +            (cs->nr_threads <= 2)) {

This duplicates the logic from topology_supports_topoext().  Why
not just call
  topology_supports_topoext(cs->nr_cores, cs->nr_threads, NULL)
here?

> +            env->features[FEAT_8000_0001_ECX] |= CPUID_EXT3_TOPOEXT;
> +        }
> +    }
> +
> +    if ((env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_TOPOEXT) &&
> +        !topology_supports_topoext(cs->nr_cores, cs->nr_threads, errp)) {
> +        return;
> +    }
> +
>      /* Only Intel CPUs support hyperthreading. Even though QEMU fixes this
>       * issue by adjusting CPUID_0000_0001_EBX and CPUID_8000_0008_ECX
>       * based on inputs (sockets,cores,threads), it is still better to gives
> -- 
> 1.8.3.1
> 

-- 
Eduardo