Re: [Qemu-devel] [PATCH V3] target-i386: forward CPUID cache leaves when -cpu host is used

[Paolo Bonzini <pbonzini@redhat.com>]

Il 02/09/2013 17:06, Benoît Canet ha scritto:
> Some users running cpu intensive tasks checking the cache CPUID leaves at
> startup and making decisions based on the result reported that the guest was
> not reflecting the host CPUID leaves when -cpu host is used.
> 
> This patch fix this.
> 
> Signed-off-by: Benoit Canet <benoit@irqsave.net>
> ---
>  target-i386/cpu-qom.h |    3 +++
>  target-i386/cpu.c     |   19 +++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
> index c4447c2..b1d1bd8 100644
> --- a/target-i386/cpu-qom.h
> +++ b/target-i386/cpu-qom.h
> @@ -70,6 +70,9 @@ typedef struct X86CPU {
>      bool hyperv_relaxed_timing;
>      int hyperv_spinlock_attempts;
>  
> +    /* if true the CPUID code directly forward host cache leaves to the guest */
> +    bool fwd_host_cache_info;
> +
>      /* Features that were filtered out because of missing host capabilities */
>      uint32_t filtered_features[FEATURE_WORDS];
>  
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index c36345e..f0df4db 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -486,6 +486,7 @@ typedef struct x86_def_t {
>      int stepping;
>      FeatureWordArray features;
>      char model_id[48];
> +    bool fwd_host_cache_info;
>  } x86_def_t;
>  
>  #define I486_FEATURES (CPUID_FP87 | CPUID_VME | CPUID_PSE)
> @@ -1139,6 +1140,7 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
>      assert(kvm_enabled());
>  
>      x86_cpu_def->name = "host";
> +    x86_cpu_def->fwd_host_cache_info = true;
>      host_cpuid(0x0, 0, &eax, &ebx, &ecx, &edx);
>      x86_cpu_vendor_words2str(x86_cpu_def->vendor, ebx, edx, ecx);
>  
> @@ -1888,6 +1890,7 @@ static void cpu_x86_register(X86CPU *cpu, const char *name, Error **errp)
>      env->features[FEAT_C000_0001_EDX] = def->features[FEAT_C000_0001_EDX];
>      env->features[FEAT_7_0_EBX] = def->features[FEAT_7_0_EBX];
>      env->cpuid_xlevel2 = def->xlevel2;
> +    cpu->fwd_host_cache_info = def->fwd_host_cache_info;
>  
>      object_property_set_str(OBJECT(cpu), def->model_id, "model-id", errp);
>  }
> @@ -2062,6 +2065,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>          break;
>      case 2:
>          /* cache info: needed for Pentium Pro compatibility */
> +        if (cpu->fwd_host_cache_info) {
> +            host_cpuid(index, 0, eax, ebx, ecx, edx);
> +            break;
> +        }
>          *eax = 1; /* Number of CPUID[EAX=2] calls required */
>          *ebx = 0;
>          *ecx = 0;
> @@ -2071,6 +2078,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>          break;
>      case 4:
>          /* cache info: needed for Core compatibility */
> +        if (cpu->fwd_host_cache_info) {
> +            host_cpuid(index, count, eax, ebx, ecx, edx);
> +            break;
> +        }
>          if (cs->nr_cores > 1) {
>              *eax = (cs->nr_cores - 1) << 26;
>          } else {
> @@ -2228,6 +2239,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>          break;
>      case 0x80000005:
>          /* cache info (L1 cache) */
> +        if (cpu->fwd_host_cache_info) {
> +            host_cpuid(index, 0, eax, ebx, ecx, edx);
> +            break;
> +        }
>          *eax = (L1_DTLB_2M_ASSOC << 24) | (L1_DTLB_2M_ENTRIES << 16) | \
>                 (L1_ITLB_2M_ASSOC <<  8) | (L1_ITLB_2M_ENTRIES);
>          *ebx = (L1_DTLB_4K_ASSOC << 24) | (L1_DTLB_4K_ENTRIES << 16) | \
> @@ -2239,6 +2254,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>          break;
>      case 0x80000006:
>          /* cache info (L2 cache) */
> +        if (cpu->fwd_host_cache_info) {
> +            host_cpuid(index, 0, eax, ebx, ecx, edx);
> +            break;
> +        }
>          *eax = (AMD_ENC_ASSOC(L2_DTLB_2M_ASSOC) << 28) | \
>                 (L2_DTLB_2M_ENTRIES << 16) | \
>                 (AMD_ENC_ASSOC(L2_ITLB_2M_ASSOC) << 12) | \
> 

I renamed the new field to cache_info_passthrough (Eduardo had a
"pmu_passthrough" patch a few weeks ago) and will push it tomorrow to
uq/master.  Thanks,

Paolo