Re: [Qemu-devel] [PATCH 06/17] target-i386: remove vendor_override field from CPUX86State

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 11 Jan 2013 00:42:13 -0200
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Fri, Jan 11, 2013 at 03:10:20AM +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.
> > 
> > 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
> > 
> 
> How do you plan to make this work when the vendor string for each model
> gets represented using a default defined at class_init-time[1]? When we do
it could be done by late update hook like you did for host cpu subclass or
forcing early kvm_init() and then do it at class_init-time. I still hope that
second option would work(but I haven't checked yet).

> that, we wouldn't be able to differentiate the built/predefined vendor
> value (used for TCG only) and the user-defined vendor value (that would
> be set in KVM mode too).
If we have subclasses with already correct vendor for a specific mode then we
needn't to know if it is built-in vendor or user-defined.

> 
> [1] AFAIU, class_init would never be able to check kvm_enabled(), by
> design, because it may run before anything is configured (even the
> choice to enable/disable KVM).
> 
> Maybe we can later add a "tcg-vendor" property, that would override the
> vendor only if in TCG mode. Then the predefined CPU models could have a
> "tcg-vendor" default set, and no "vendor" default set, to emulate the
> current behavior.
> 
> > '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 <imammedo@redhat.com>
> > ---
> >  v4:
> >    - rebased with "target-i386: move out CPU features initialization
> >      in separate func" dropped. So remove vendor_override in
> >      cpu_x86_register() instead.
> >    - replace x86cpu_vendor_words2str() with x86_cpu_vendor_words2str()
> >      due to renaming of the last in previous patch
> > ---
> >  target-i386/cpu.c |   27 ++++++++++++---------------
> >  target-i386/cpu.h |    1 -
> >  2 files changed, 12 insertions(+), 16 deletions(-)
> > 
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index 0b4fa57..4250c77 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -362,7 +362,6 @@ 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;
> > @@ -934,7 +933,6 @@ 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;
> >  
> >      /* Call Centaur's CPUID instruction. */
> >      if (!strcmp(x86_cpu_def->vendor, CPUID_VENDOR_VIA)) {
> > @@ -1201,7 +1199,6 @@ 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)
> > @@ -1287,6 +1284,18 @@ 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));
> > +        /* 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 using the 'vendor' property if you want to use KVM's
> > +         * sysenter/syscall emulation in compatibility mode and when doing
> > +         * cross vendor migration
> > +         */
> > +        if (kvm_enabled()) {
> > +            uint32_t  ebx = 0, ecx = 0, edx = 0;
> > +            host_cpuid(0, 0, NULL, &ebx, &ecx, &edx);
> > +            x86_cpu_vendor_words2str(x86_cpu_def->vendor, ebx, edx, ecx);
> > +        }
> >      }
> >  
> >      return 0;
> > @@ -1358,7 +1367,6 @@ 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);
> > @@ -1554,7 +1562,6 @@ int cpu_x86_register(X86CPU *cpu, const char *cpu_model)
> >      }
> >      assert(def->vendor[0]);
> >      object_property_set_str(OBJECT(cpu), def->vendor, "vendor", &error);
> > -    env->cpuid_vendor_override = def->vendor_override;
> >      object_property_set_int(OBJECT(cpu), def->level, "level", &error);
> >      object_property_set_int(OBJECT(cpu), def->family, "family", &error);
> >      object_property_set_int(OBJECT(cpu), def->model, "model", &error);
> > @@ -1626,16 +1633,6 @@ 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 983aab1..8bb5a58 100644
> > --- a/target-i386/cpu.h
> > +++ b/target-i386/cpu.h
> > @@ -829,7 +829,6 @@ 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;
> > -- 
> > 1.7.1
> > 
> 
> -- 
> Eduardo


-- 
Regards,
  Igor