Re: [Qemu-devel] [PATCH 13/20] target-i386: remove vendor_override field from CPUX86State

[Igor Mammedov]

On Thu, 20 Dec 2012 10:48:08 -0200
Eduardo Habkost <address@hidden> wrote:

> On Thu, Dec 20, 2012 at 01:16:31AM +0100, Igor Mammedov wrote:
> > commit 8935499831312 makes cpuid return to guest host's vendor value
> > instead of built-in one by default if kvm_enabled() == true and allows
> > to override this behavior if 'vendor' is specified on -cpu command line.
> > 
> > But every time guest calls cpuid to get 'vendor' value, host's value is
> > read again and again in default case.
> > 
> > It complicates semantic of vendor property and makes it harder to use,
> > due to split brain syndrome, lets simplify it.
> > 
> > Instead of reading 'vendor' value from host every time cpuid[vendor] is
> > called, override 'vendor' value only once in cpu_x86_find_by_name(), when
> > built-in CPU model is found and if(kvm_enabled() == true).
> > 
> > It provides the same default semantic
> >  if (kvm_enabled() == true)  vendor = host's vendor
> >  else vendor = built-in vendor
> > 
> > and then later:
> >  if (custom vendor) vendor = custom vendor
> > 
> > 'vendor' value is overridden when user provides it on -cpu command line,
> > and there isn't need in vendor_override field anymore, remove it.
> > 
> > Signed-off-by: Igor Mammedov <address@hidden>
> > ---
> >  target-i386/cpu.c | 20 +++++---------------
> >  target-i386/cpu.h |  1 -
> >  2 files changed, 5 insertions(+), 16 deletions(-)
> > 
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index a96aa33..a12d938 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -284,7 +284,6 @@ typedef struct x86_def_t {
> >      uint32_t kvm_features, svm_features;
> >      uint32_t xlevel;
> >      char model_id[48];
> > -    int vendor_override;
> >      /* Store the results of Centaur's CPUID instructions */
> >      uint32_t ext4_features;
> >      uint32_t xlevel2;
> 
> 
> > @@ -865,7 +864,6 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
> >                  kvm_arch_get_supported_cpuid(s, 0x80000001, 0, R_ECX);
> >  
> >      cpu_x86_fill_model_id(x86_cpu_def->model_id);
> > -    x86_cpu_def->vendor_override = 0;
> >  
> 
> It's funny how x86_def_t _never_ has vendor_override set to true. The
> field was completely pointless.
> 
> 
> >      /* Call Centaur's CPUID instruction. */
> >      if (!strcmp(x86_cpu_def->vendor, CPUID_VENDOR_VIA)) {
> > @@ -1117,7 +1115,6 @@ static void x86_cpuid_set_vendor(Object *obj, const
> > char *value, env->cpuid_vendor2 |= ((uint8_t)value[i + 4]) << (8 * i);
> >          env->cpuid_vendor3 |= ((uint8_t)value[i + 8]) << (8 * i);
> >      }
> > -    env->cpuid_vendor_override = 1;
> >  }
> >  
> >  static char *x86_cpuid_get_model_id(Object *obj, Error **errp)
> > @@ -1194,7 +1191,6 @@ static void cpudef_2_x86_cpu(X86CPU *cpu, x86_def_t
> > *def, Error **errp) 
> >      assert(def->vendor[0]);
> >      object_property_set_str(OBJECT(cpu), def->vendor, "vendor", errp);
> > -    env->cpuid_vendor_override = def->vendor_override;
> >      object_property_set_int(OBJECT(cpu), def->level, "level", errp);
> >      object_property_set_int(OBJECT(cpu), def->family, "family", errp);
> >      object_property_set_int(OBJECT(cpu), def->model, "model", errp);
> > @@ -1231,6 +1227,11 @@ static int cpu_x86_find_by_name(x86_def_t
> > *x86_cpu_def, const char *name) return -1;
> >      } else {
> >          memcpy(x86_cpu_def, def, sizeof(*def));
> 
> Could you keep the old comment explaining the reason for the KVM
> behavior, here?
> 
> /* sysenter isn't supported on compatibility mode on AMD, syscall
>  * isn't supported in compatibility mode on Intel.
>  * Normally we advertise the actual cpu vendor, but you can override
>  * this if you want to use KVM's sysenter/syscall emulation
>  * in compatibility mode and when doing cross vendor migration
>  */
> 
> (I suggest replacing "you can override this" with "you can override this
> using the 'vendor' property").
sure, I'll do it on series respin.


> 
> The rest of the patch looks good to me.
> 
> 
> > +        if (kvm_enabled()) {
> > +            uint32_t  ebx = 0, ecx = 0, edx = 0;
> > +            host_cpuid(0, 0, NULL, &ebx, &ecx, &edx);
> > +            x86cpu_vendor_words2str(x86_cpu_def->vendor, ebx, edx, ecx);
> > +        }
> 
> I like the fact that you are doing this as early as possible (even
> before cpudef_2_x86_cpu() is called), making it easy to move the logic
> to class_init.
> 
> 
> >      }
> >  
> >      return 0;
> > @@ -1331,7 +1332,6 @@ static int cpu_x86_parse_featurestr(x86_def_t
> > *x86_cpu_def, char *features, x86_cpu_def->xlevel = numvalue;
> >              } else if (!strcmp(featurestr, "vendor")) {
> >                  pstrcpy(x86_cpu_def->vendor,
> > sizeof(x86_cpu_def->vendor), val);
> > -                x86_cpu_def->vendor_override = 1;
> >              } else if (!strcmp(featurestr, "model_id")) {
> >                  pstrcpy(x86_cpu_def->model_id,
> > sizeof(x86_cpu_def->model_id), val);
> > @@ -1582,16 +1582,6 @@ static void get_cpuid_vendor(CPUX86State *env,
> > uint32_t *ebx, *ebx = env->cpuid_vendor1;
> >      *edx = env->cpuid_vendor2;
> >      *ecx = env->cpuid_vendor3;
> > -
> > -    /* sysenter isn't supported on compatibility mode on AMD, syscall
> > -     * isn't supported in compatibility mode on Intel.
> > -     * Normally we advertise the actual cpu vendor, but you can override
> > -     * this if you want to use KVM's sysenter/syscall emulation
> > -     * in compatibility mode and when doing cross vendor migration
> > -     */
> > -    if (kvm_enabled() && ! env->cpuid_vendor_override) {
> > -        host_cpuid(0, 0, NULL, ebx, ecx, edx);
> > -    }
> >  }
> >  
> >  void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> > diff --git a/target-i386/cpu.h b/target-i386/cpu.h
> > index fbbe730..a15a09e 100644
> > --- a/target-i386/cpu.h
> > +++ b/target-i386/cpu.h
> > @@ -812,7 +812,6 @@ typedef struct CPUX86State {
> >      uint32_t cpuid_ext2_features;
> >      uint32_t cpuid_ext3_features;
> >      uint32_t cpuid_apic_id;
> > -    int cpuid_vendor_override;
> >      /* Store the results of Centaur's CPUID instructions */
> >      uint32_t cpuid_xlevel2;
> >      uint32_t cpuid_ext4_features;
> > -- 
> > 1.7.11.7
> > 
>