Re: [PATCH v11 4/5] i386: Enable TOPOEXT feature on AMD EPYC CPU

Eduardo Habkost
2018-06-05T02:57:13Z

On Thu, May 24, 2018 at 11:43:33AM -0400, Babu Moger wrote:
> Enable TOPOEXT feature on EPYC CPU. This is required to support
> hyperthreading on VM guests. Also extend xlevel to 0x8000001E.
>
> Disable TOPOEXT feature for legacy machines and also disable
> TOPOEXT feature if the config cannot be supported.
>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
> include/hw/i386/pc.h | 4 ++++
> target/i386/cpu.c | 37 +++++++++++++++++++++++++++++++++++--
> 2 files changed, 39 insertions(+), 2 deletions(-)
>
> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> index a0c269f..9c8db3d 100644
> --- a/include/hw/i386/pc.h
> +++ b/include/hw/i386/pc.h
> @@ -302,6 +302,10 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
> .driver = TYPE_X86_CPU,\
> .property = "legacy-cache",\
> .value = "on",\
> + },{\
> + .driver = "EPYC-" TYPE_X86_CPU,\
> + .property = "topoext",\
> + .value = "off",\
> },
>
> #define PC_COMPAT_2_11 \
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 9f8bad9..0b62356 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -486,6 +486,20 @@ static void encode_topo_cpuid8000001e(CPUState *cs, X86CPU *cpu,
> }
>
> /*
> + * 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 verify_topology(int nr_cores, int nr_threads)

I suggest using a more descriptive name, like
"topology_supports_topoext()".

> +{
> + if ((nr_cores > (MAX_CORES_IN_NODE * MAX_NODES_PER_SOCKET)) ||
> + (nr_threads > 2)) {
> + return 0;

Oh, this is what I was looking for, on the previous patches. I
suggest moving this to a separate patch, separate from the patch
that changes the EPYC CPU model.

> + }
> + return 1;
> +}
> +
> +/*
> * Definitions of the hardcoded cache entries we expose:
> * These are legacy cache values. If there is a need to change any
> * of these values please use builtin_x86_defs
> @@ -2531,7 +2545,8 @@ 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 |
> @@ -2576,7 +2591,8 @@ 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] =
> @@ -4156,6 +4172,12 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> break;
> case 0x8000001D:
> *eax = 0;
> + /* Check if we can support this topology */
> + if (!verify_topology(cs->nr_cores, cs->nr_threads)) {
> + /* Disable topology extention */
> + env->features[FEAT_8000_0001_ECX] &= !CPUID_EXT3_TOPOEXT;
> + break;

Please don't change CPUX86State inside cpu_x86_cpuid(). This
belongs to x86_cpu_realizefn().

Also, we want this:
"-cpu EPYC -smp cores=64"
to not error out, because it's a supported configuration today.

But this:
"-cpu EPYC,+topoext -smp cores=64"
should error out because the user explicitly requested an
unsupported configuration.

You can implement this by checking if TOPOEXT is set on
env->user_features.

> + }
> switch (count) {
> case 0: /* L1 dcache info */
> encode_cache_cpuid8000001d(env->cache_info_amd.l1d_cache, cs,
> @@ -4180,6 +4202,12 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> break;
> case 0x8000001E:
> assert(cpu->core_id <= 255);
> + /* Check if we can support this topology */
> + if (!verify_topology(cs->nr_cores, cs->nr_threads)) {
> + /* Disable topology extention */
> + env->features[FEAT_8000_0001_ECX] &= !CPUID_EXT3_TOPOEXT;
> + break;
> + }
> encode_topo_cpuid8000001e(cs, cpu,
> eax, ebx, ecx, edx);
> break;
> @@ -4644,6 +4672,11 @@ 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);
> + }
> +
> /* SEV requires CPUID[0x8000001F] */
> if (sev_enabled()) {
> x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, 0x8000001F);
> --
> 1.8.3.1
>
>

--
Eduardo