Re: [Qemu-devel] [PATCH] target-i386: Disable cache info passthrough by default

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 19 Aug 2015 10:08:22 -0700
Eduardo Habkost <ehabkost@redhat.com> wrote:

> The host cache information may not make sense for the guest if the VM
> CPU topology doesn't match the host CPU topology. To make sure we won't
> expose broken cache information to the guest, disable cache info
> passthrough by default, and add a new "host-cache-info" property that
> can be used to enable the old behavior for users that really need it.
> 
> Cc: Benoît Canet <benoit@irqsave.net>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
>  target-i386/cpu.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index cfb8aa7..3a71f15 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -689,7 +689,6 @@ struct X86CPUDefinition {
>      int stepping;
>      FeatureWordArray features;
>      char model_id[48];
> -    bool cache_info_passthrough;
>  };
>  
>  static X86CPUDefinition builtin_x86_defs[] = {
> @@ -1416,6 +1415,7 @@ static X86CPUDefinition host_cpudef;
>  
>  static Property host_x86_cpu_properties[] = {
>      DEFINE_PROP_BOOL("migratable", X86CPU, migratable, true),
> +    DEFINE_PROP_BOOL("host-cache-info", X86CPU, cache_info_passthrough, false),
>      DEFINE_PROP_END_OF_LIST()
>  };
>  
> @@ -1442,7 +1442,6 @@ static void host_x86_cpu_class_init(ObjectClass *oc, void *data)
>      cpu_x86_fill_model_id(host_cpudef.model_id);
>  
>      xcc->cpu_def = &host_cpudef;
> -    host_cpudef.cache_info_passthrough = true;
>  
>      /* level, xlevel, xlevel2, and the feature words are initialized on
>       * instance_init, because they require KVM to be initialized.
> @@ -2076,7 +2075,6 @@ static void x86_cpu_load_def(X86CPU *cpu, X86CPUDefinition *def, Error **errp)
>      object_property_set_int(OBJECT(cpu), def->stepping, "stepping", errp);
>      object_property_set_int(OBJECT(cpu), def->xlevel, "xlevel", errp);
>      object_property_set_int(OBJECT(cpu), def->xlevel2, "xlevel2", errp);
> -    cpu->cache_info_passthrough = def->cache_info_passthrough;
Isn't that a guest visible change?

>      object_property_set_str(OBJECT(cpu), def->model_id, "model-id", errp);
>      for (w = 0; w < FEATURE_WORDS; w++) {
>          env->features[w] = def->features[w];