Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Jun 08, 2018 at 06:56:19PM -0400, Babu Moger wrote:
> Enable TOPOEXT feature on EPYC CPU. This is required to support
> hyperthreading on VM guests. Also extend xlevel to 0x8000001E.
> 
> TOPOEXT feature is disabled for legacy machines.
> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
>  target/i386/cpu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index d3411ed..4dd9a82 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -2574,6 +2574,7 @@ static X86CPUDefinition builtin_x86_defs[] = {
>          .xlevel = 0x8000000A,
>          .model_id = "AMD EPYC Processor",
>          .cache_info = &epyc_cache_info,
> +        .auto_topoext = 1,
>      },
>      {
>          .name = "EPYC-IBPB",
> @@ -2621,6 +2622,7 @@ static X86CPUDefinition builtin_x86_defs[] = {
>          .xlevel = 0x8000000A,
>          .model_id = "AMD EPYC Processor (with IBPB)",
>          .cache_info = &epyc_cache_info,
> +        .auto_topoext = 1,
>      },
>  };
>  
> @@ -4672,6 +4674,11 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
>              x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, 0x8000000A);
>          }
>  
> +        /* TOPOEXT feature requires 0x8000001E */
> +        if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_TOPOEXT) {
> +            x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, 0x8000001E);
> +        }

I suggest moving this hunk to a separate patch.  I'm not 100%
sure yet if this will require compat_props code to disable
auto-xlevel-increase on older machine-types.

-- 
Eduardo