Re: [Qemu-devel] [PATCH v14 2/6] i386: Enable TOPOEXT feature on AMD EPYC CPU

[Eduardo Habkost <ehabkost@redhat.com>]

On Wed, Jun 13, 2018 at 09:18:23PM -0400, Babu Moger wrote:
> Enable TOPOEXT feature on EPYC CPU. This is required to support
> hyperthreading on VM guests. Also extend xlevel to 0x8000001E.
> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
>  target/i386/cpu.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 86fb1a4..2eb26da 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -2554,7 +2554,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
>          .features[FEAT_8000_0001_ECX] =
>              CPUID_EXT3_OSVW | CPUID_EXT3_3DNOWPREFETCH |
>              CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A | CPUID_EXT3_ABM |
> -            CPUID_EXT3_CR8LEG | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,
> +            CPUID_EXT3_CR8LEG | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM |
> +            CPUID_EXT3_TOPOEXT,
>          .features[FEAT_7_0_EBX] =
>              CPUID_7_0_EBX_FSGSBASE | CPUID_7_0_EBX_BMI1 | CPUID_7_0_EBX_AVX2 |
>              CPUID_7_0_EBX_SMEP | CPUID_7_0_EBX_BMI2 | CPUID_7_0_EBX_RDSEED |
> @@ -2599,7 +2600,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
>          .features[FEAT_8000_0001_ECX] =
>              CPUID_EXT3_OSVW | CPUID_EXT3_3DNOWPREFETCH |
>              CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A | CPUID_EXT3_ABM |
> -            CPUID_EXT3_CR8LEG | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,
> +            CPUID_EXT3_CR8LEG | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM |
> +            CPUID_EXT3_TOPOEXT,
>          .features[FEAT_8000_0008_EBX] =
>              CPUID_8000_0008_EBX_IBPB,
>          .features[FEAT_7_0_EBX] =

This part is OK, but it requires patch 3/6 to be included in the
same patch.

> @@ -4667,6 +4669,11 @@ 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);
> +        }

This part needs to be done more carefully to avoid breaking
compatibility.  "-machine pc-q35-2.12 -cpu Opteron_G5,+topoext"
currently results in xlevel=0x8000001A, and this must not change.

I suggest just changing setting .xlevel=0x8000001E on EPYC at
builtin_x86_defs[1], and worry about automatically increasing
xlevel later.

(If you change EPYC.xlevel in builtin_x86_defs, don't forget to
set EPYC.xlevel=0x8000000A on PC_COMPAT_2_12)

-- 
Eduardo