Re: [Qemu-devel] [RFC 11/20] target-i386: convert 'check' and 'enforce' features into properties

[Eduardo Habkost]

On Fri, Aug 10, 2012 at 01:22:27PM +0200, Igor Mammedov wrote:
> Signed-off-by: Igor Mammedov <address@hidden>
> ---
>  target-i386/cpu.c | 68 
> ++++++++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 57 insertions(+), 11 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 7734613..a154e89 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -106,8 +106,8 @@ typedef struct model_features_t {
>      uint32_t cpuid;
>      } model_features_t;
>  
> -int check_cpuid = 0;
> -int enforce_cpuid = 0;
> +bool check_cpuid;
> +bool enforce_cpuid;
>  
>  void host_cpuid(uint32_t function, uint32_t count,
>                  uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx)
> @@ -579,19 +579,20 @@ static int unavailable_host_feature(struct 
> model_features_t *f, uint32_t mask)
>   * their way to the guest.  Note: ft[].check_feat ideally should be
>   * specified via a guest_def field to suppress report of extraneous flags.
>   */
> -static int check_features_against_host(x86_def_t *guest_def)
> +static int check_features_against_host(X86CPU *cpu)
>  {
> +    CPUX86State *env = &cpu->env;
>      x86_def_t host_def;
>      uint32_t mask;
>      int rv, i;
>      struct model_features_t ft[] = {
> -        {&guest_def->features, &host_def.features,
> +        {&env->cpuid_features, &host_def.features,
>              ~0, feature_name, 0x00000000},
> -        {&guest_def->ext_features, &host_def.ext_features,
> +        {&env->cpuid_ext_features, &host_def.ext_features,
>              ~CPUID_EXT_HYPERVISOR, ext_feature_name, 0x00000001},
> -        {&guest_def->ext2_features, &host_def.ext2_features,
> +        {&env->cpuid_ext2_features, &host_def.ext2_features,
>              ~PPRO_FEATURES, ext2_feature_name, 0x80000000},
> -        {&guest_def->ext3_features, &host_def.ext3_features,
> +        {&env->cpuid_ext3_features, &host_def.ext3_features,
>              ~CPUID_EXT3_SVM, ext3_feature_name, 0x80000001}};
>  
>      cpu_x86_fill_host(&host_def);
> @@ -1030,6 +1031,43 @@ static void x86_set_hv_vapic(Object *obj, Visitor *v, 
> void *opaque,
>  }
>  #endif
>  
> +static void x86_cpuid_get_check(Object *obj, Visitor *v, void *opaque,
> +                                         const char *name, Error **errp)
> +{
> +    visit_type_bool(v, &check_cpuid, name, errp);
> +}
> +
> +static void x86_cpuid_set_check(Object *obj, Visitor *v, void *opaque,
> +                                         const char *name, Error **errp)
> +{
> +    bool value;
> +
> +    visit_type_bool(v, &value, name, errp);
> +    if (error_is_set(errp)) {
> +        return;
> +    }
> +    check_cpuid = value;
> +}
> +
> +static void x86_cpuid_get_enforce(Object *obj, Visitor *v, void *opaque,
> +                                         const char *name, Error **errp)
> +{
> +    visit_type_bool(v, &enforce_cpuid, name, errp);
> +}
> +
> +static void x86_cpuid_set_enforce(Object *obj, Visitor *v, void *opaque,
> +                                         const char *name, Error **errp)
> +{
> +    bool value;
> +
> +    visit_type_bool(v, &value, name, errp);
> +    if (error_is_set(errp)) {
> +        return;
> +    }
> +    enforce_cpuid = value;
> +    object_property_set_bool(obj, value, "check", errp);
> +}
> +
>  static void cpudef_2_x86_cpu(X86CPU *cpu, x86_def_t *def, Error **errp)
>  {
>      CPUX86State *env = &cpu->env;
> @@ -1225,10 +1263,6 @@ static int cpu_x86_find_by_name(X86CPU *cpu, x86_def_t 
> *x86_cpu_def,
>      x86_cpu_def->ext3_features &= ~minus_ext3_features;
>      x86_cpu_def->kvm_features &= ~minus_kvm_features;
>      x86_cpu_def->svm_features &= ~minus_svm_features;
> -    if (check_cpuid) {
> -        if (check_features_against_host(x86_cpu_def) && enforce_cpuid)
> -            goto error;
> -    }
>      g_free(s);
>      return 0;
>  
> @@ -1923,6 +1957,12 @@ void x86_cpu_realize(Object *obj, Error **errp)
>          env->cpuid_svm_features &= TCG_SVM_FEATURES;
>      }
>  
> +    if (check_cpuid && check_features_against_host(cpu)
> +        && enforce_cpuid) {
> +        error_set(errp, QERR_PERMISSION_DENIED);
> +        return;
> +    }
> +

I just noticed that you changed behavior on patch 04/20 and now restore
the behavior in this patch:

- Before patch 04/20, the feature check was being done after the
  features were filtered according to the TCG support (meaning a feature
  not supported by TCG will not trigger enforce/check errors).
- After patch 04/20, the check was being done _before_ the features were
  filtered according to TCG support (meaning a feature not supported by
  TCG would trigger enforce/check errors).
- With this patch, the old behavior is restored.

I'm not sure which behavior is better. But we surely shouldn't silently
move back and forth between those two modes.

IMO, checking _before_ the TCG filtering is better, as it's more
predictable. it means having lots of warnings in case too-new CPU models
are chosen in TCG model, but that's exactly the point.


>  #ifndef CONFIG_USER_ONLY
>      qemu_register_reset(x86_cpu_machine_reset_cb, cpu);
>  #endif
> @@ -1964,6 +2004,12 @@ static void x86_cpu_initfn(Object *obj)
>      object_property_add(obj, "tsc-frequency", "int",
>                          x86_cpuid_get_tsc_freq,
>                          x86_cpuid_set_tsc_freq, NULL, NULL, NULL);
> +    object_property_add(obj, "check", "bool",
> +                        x86_cpuid_get_check,
> +                        x86_cpuid_set_check, NULL, NULL, NULL);
> +    object_property_add(obj, "enforce", "bool",
> +                        x86_cpuid_get_enforce,
> +                        x86_cpuid_set_enforce, NULL, NULL, NULL);
>  #if !defined(CONFIG_USER_ONLY)
>      object_property_add(obj, "hv_spinlocks", "int",
>                          x86_get_hv_spinlocks,
> -- 
> 1.7.11.2
> 

-- 
Eduardo