Re: [Qemu-devel] [PATCH] target-i386: Support migratable=no properly

[Eduardo Habkost]

Forgot to add qemu-devel to "To:". Adding it.

On Wed, Aug 20, 2014 at 05:30:12PM -0300, Eduardo Habkost wrote:
> When the "migratable" property was implemented, the behavior was tested
> by changing the default on the code, but actually using the option on
> the command-line (e.g. "-cpu host,migratable=false") doesn't work as
> expected. This is a regression for a common use case of "-cpu host",
> which is to enable features that are supported by the host CPU + kernel
> before feature-specific code is added to QEMU.
> 
> Fix this by initializing the feature words for "-cpu host" on
> x86_cpu_parse_featurestr(), right after parsing the CPU options.
> 
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---
> I was considering a more complex (but less hacky) fix, by introducing an
> enum FeatureBit { OFF, ON, HOST }, making FeatureWord a 32-element
> FeatureBit array, and initializing the actual feature bits on
> x86_cpu_realizefn(). But as this is a patch for qemu-stable, I kept the
> fix as simple as possible.
> ---
>  target-i386/cpu-qom.h |  1 +
>  target-i386/cpu.c     | 17 ++++++++++++-----
>  2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
> index 71a1b97..7755466 100644
> --- a/target-i386/cpu-qom.h
> +++ b/target-i386/cpu-qom.h
> @@ -92,6 +92,7 @@ typedef struct X86CPU {
>      bool enforce_cpuid;
>      bool expose_kvm;
>      bool migratable;
> +    bool host_features;
>  
>      /* if true the CPUID code directly forward host cache leaves to the 
> guest */
>      bool cache_info_passthrough;
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 6d008ab..c0f8efc 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -1318,18 +1318,18 @@ static void host_x86_cpu_initfn(Object *obj)
>      X86CPU *cpu = X86_CPU(obj);
>      CPUX86State *env = &cpu->env;
>      KVMState *s = kvm_state;
> -    FeatureWord w;
>  
>      assert(kvm_enabled());
>  
> +    /* We can't fill the features array here because we don't know yet if
> +     * "migratable" is true or false.
> +     */
> +    cpu->host_features = true;
> +
>      env->cpuid_level = kvm_arch_get_supported_cpuid(s, 0x0, 0, R_EAX);
>      env->cpuid_xlevel = kvm_arch_get_supported_cpuid(s, 0x80000000, 0, 
> R_EAX);
>      env->cpuid_xlevel2 = kvm_arch_get_supported_cpuid(s, 0xC0000000, 0, 
> R_EAX);
>  
> -    for (w = 0; w < FEATURE_WORDS; w++) {
> -        env->features[w] =
> -            x86_cpu_get_supported_feature_word(w, cpu->migratable);
> -    }
>      object_property_set_bool(OBJECT(cpu), true, "pmu", &error_abort);
>  }
>  
> @@ -1828,6 +1828,13 @@ static void x86_cpu_parse_featurestr(CPUState *cs, 
> char *features,
>          featurestr = strtok(NULL, ",");
>      }
>  
> +    if (cpu->host_features) {
> +        for (w = 0; w < FEATURE_WORDS; w++) {
> +            env->features[w] =
> +                x86_cpu_get_supported_feature_word(w, cpu->migratable);
> +        }
> +    }
> +
>      for (w = 0; w < FEATURE_WORDS; w++) {
>          env->features[w] |= plus_features[w];
>          env->features[w] &= ~minus_features[w];
> -- 
> 1.9.3
> 

-- 
Eduardo