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

[Eduardo Habkost]

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
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).

[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 <address@hidden>
> ---
>  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