Re: [Qemu-devel] [PATCH] target-i386: warns users when CPU threads>1 for AMD CPUs

[Paolo Bonzini]

On 10/21/2014 05:00 PM, Wei Huang wrote:
> No AMD CPUs support hyperthreading. When users select threads>1 in
> -smp option, QEMU fixes it by adjusting CPUID_0000_0001_EBX and
> CPUID_8000_0008_ECX based on inputs (sockets, cores, threads);
> so guest VM can boot correctly. However it is still better to gives
> users a warning when such case happens.
> 
> Signed-off-by: Wei Huang <address@hidden>

Tweaked as suggested by Eduardo, and applied.

Paolo

> ---
>  target-i386/cpu.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index e7bf9de..84cbbcd 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -2696,6 +2696,10 @@ static void x86_cpu_apic_realize(X86CPU *cpu, Error 
> **errp)
>  }
>  #endif
>  
> +
> +#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)
>  static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
>  {
>      CPUState *cs = CPU(dev);
> @@ -2703,6 +2707,7 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
> **errp)
>      X86CPUClass *xcc = X86_CPU_GET_CLASS(dev);
>      CPUX86State *env = &cpu->env;
>      Error *local_err = NULL;
> +    static bool ht_warned;
>  
>      if (env->features[FEAT_7_0_EBX] && env->cpuid_level < 7) {
>          env->cpuid_level = 7;
> @@ -2711,9 +2716,7 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
> **errp)
>      /* On AMD CPUs, some CPUID[8000_0001].EDX bits must match the bits on
>       * CPUID[1].EDX.
>       */
> -    if (env->cpuid_vendor1 == CPUID_VENDOR_AMD_1 &&
> -        env->cpuid_vendor2 == CPUID_VENDOR_AMD_2 &&
> -        env->cpuid_vendor3 == CPUID_VENDOR_AMD_3) {
> +    if (IS_AMD_CPU(env)) {
>          env->features[FEAT_8000_0001_EDX] &= ~CPUID_EXT2_AMD_ALIASES;
>          env->features[FEAT_8000_0001_EDX] |= (env->features[FEAT_1_EDX]
>             & CPUID_EXT2_AMD_ALIASES);
> @@ -2742,6 +2745,20 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
> **errp)
>      mce_init(cpu);
>      qemu_init_vcpu(cs);
>  
> +    /* AMD CPU doesn't 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
> +     * users a warning.
> +     *
> +     * NOTE: the following code has to follow qemu_init_vcpu(). Otherwise
> +     * cs->nr_threads hasn't be populated yet and the checking is incorrect.
> +     */
> +    if (IS_AMD_CPU(env) && (cs->nr_threads > 1) && !ht_warned) {
> +        error_report("AMD CPU doesn't support hyperthreading. Please 
> configure"
> +                     " -smp options properly.");
> +        ht_warned = true;
> +    }
> +
>      x86_cpu_apic_realize(cpu, &local_err);
>      if (local_err != NULL) {
>          goto out;
>