[Qemu-devel] [PATCH] target-i386: add AMD CPUID.1:edx aliases to x86_cpu_get_migratable_flags

[Qemu-devel] [PATCH] target-i386: add AMD CPUID.1:edx aliases to x86_cpu_get_migratable_flags

[Radim Krčmář]

QEMU complains about -cpu host on an AMD machine:
  warning: host doesn't support requested feature: CPUID.80000001H:EDX [bit 0]
For bits 0,1,3,4,5,6,7,8,9,12,13,14,15,16,17,23,24.

Host does support them, but x86_cpu_get_migratable_flags filters unnamed
features and drops these bits without realizing that they are aliases to
CPUID.1H:EDX and have their names there.

See https://bugzilla.redhat.com/show_bug.cgi?id=1326721 for details.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 target-i386/cpu.c | 40 ++++++++++++++++++++++------------------
 1 file changed, 22 insertions(+), 18 deletions(-)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index ddae932ee1b4..66bd9d0c4039 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -506,7 +506,7 @@ const char *get_register_name_32(unsigned int reg)
  * Returns the set of feature flags that are supported and migratable by
  * QEMU, for a given FeatureWord.
  */
-static uint32_t x86_cpu_get_migratable_flags(FeatureWord w)
+static uint32_t x86_cpu_get_migratable_flags(FeatureWord w, bool is_amd)
 {
     FeatureWordInfo *wi = &feature_word_info[w];
     uint32_t r = 0;
@@ -514,12 +514,18 @@ static uint32_t x86_cpu_get_migratable_flags(FeatureWord w)
 
     for (i = 0; i < 32; i++) {
         uint32_t f = 1U << i;
+        FeatureWordInfo *effective_wi = wi;
+
+        if (is_amd && w == FEAT_8000_0001_EDX && f & CPUID_EXT2_AMD_ALIASES) {
+            effective_wi = &feature_word_info[FEAT_1_EDX];
+        }
+
         /* If the feature name is unknown, it is not supported by QEMU yet */
-        if (!wi->feat_names[i]) {
+        if (!effective_wi->feat_names[i]) {
             continue;
         }
         /* Skip features known to QEMU, but explicitly marked as unmigratable */
-        if (wi->unmigratable_flags & f) {
+        if (effective_wi->unmigratable_flags & f) {
             continue;
         }
         r |= f;
@@ -1423,8 +1429,7 @@ void x86_cpu_change_kvm_default(const char *prop, const char *value)
     assert(pv->prop);
 }
 
-static uint32_t x86_cpu_get_supported_feature_word(FeatureWord w,
-                                                   bool migratable_only);
+static uint32_t x86_cpu_get_supported_feature_word(FeatureWord w, X86CPU *cpu);
 
 #ifdef CONFIG_KVM
 
@@ -1974,7 +1979,7 @@ static void x86_cpu_parse_featurestr(CPUState *cs, char *features,
     if (cpu->host_features) {
         for (w = 0; w < FEATURE_WORDS; w++) {
             env->features[w] =
-                x86_cpu_get_supported_feature_word(w, cpu->migratable);
+                x86_cpu_get_supported_feature_word(w, cpu);
         }
     }
 
@@ -2050,8 +2055,14 @@ CpuDefinitionInfoList *arch_query_cpu_definitions(Error **errp)
     return cpu_list;
 }
 
-static uint32_t x86_cpu_get_supported_feature_word(FeatureWord w,
-                                                   bool migratable_only)
+#define IS_INTEL_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_INTEL_1 && \
+                           (env)->cpuid_vendor2 == CPUID_VENDOR_INTEL_2 && \
+                           (env)->cpuid_vendor3 == CPUID_VENDOR_INTEL_3)
+#define IS_AMD_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_AMD_1 && \
+                         (env)->cpuid_vendor2 == CPUID_VENDOR_AMD_2 && \
+                         (env)->cpuid_vendor3 == CPUID_VENDOR_AMD_3)
+
+static uint32_t x86_cpu_get_supported_feature_word(FeatureWord w, X86CPU *cpu)
 {
     FeatureWordInfo *wi = &feature_word_info[w];
     uint32_t r;
@@ -2065,8 +2076,8 @@ static uint32_t x86_cpu_get_supported_feature_word(FeatureWord w,
     } else {
         return ~0;
     }
-    if (migratable_only) {
-        r &= x86_cpu_get_migratable_flags(w);
+    if (cpu->migratable) {
+        r &= x86_cpu_get_migratable_flags(w, IS_AMD_CPU(&cpu->env));
     }
     return r;
 }
@@ -2084,7 +2095,7 @@ static int x86_cpu_filter_features(X86CPU *cpu)
 
     for (w = 0; w < FEATURE_WORDS; w++) {
         uint32_t host_feat =
-            x86_cpu_get_supported_feature_word(w, cpu->migratable);
+            x86_cpu_get_supported_feature_word(w, cpu);
         uint32_t requested_features = env->features[w];
         env->features[w] &= host_feat;
         cpu->filtered_features[w] = requested_features & ~env->features[w];
@@ -2872,13 +2883,6 @@ static void x86_cpu_apic_realize(X86CPU *cpu, Error **errp)
 }
 #endif
 
-
-#define IS_INTEL_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_INTEL_1 && \
-                           (env)->cpuid_vendor2 == CPUID_VENDOR_INTEL_2 && \
-                           (env)->cpuid_vendor3 == CPUID_VENDOR_INTEL_3)
-#define IS_AMD_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_AMD_1 && \
-                         (env)->cpuid_vendor2 == CPUID_VENDOR_AMD_2 && \
-                         (env)->cpuid_vendor3 == CPUID_VENDOR_AMD_3)
 static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
 {
     CPUState *cs = CPU(dev);
-- 
2.8.1

Re: [Qemu-devel] [PATCH] target-i386: add AMD CPUID.1:edx aliases to x86_cpu_get_migratable_flags

[Eduardo Habkost]

On Thu, Apr 14, 2016 at 10:55:07PM +0200, Radim Krčmář wrote:
> QEMU complains about -cpu host on an AMD machine:
>   warning: host doesn't support requested feature: CPUID.80000001H:EDX [bit 0]
> For bits 0,1,3,4,5,6,7,8,9,12,13,14,15,16,17,23,24.
> 
> Host does support them, but x86_cpu_get_migratable_flags filters unnamed
> features and drops these bits without realizing that they are aliases to
> CPUID.1H:EDX and have their names there.
> 
> See https://bugzilla.redhat.com/show_bug.cgi?id=1326721 for details.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  target-i386/cpu.c | 40 ++++++++++++++++++++++------------------
>  1 file changed, 22 insertions(+), 18 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index ddae932ee1b4..66bd9d0c4039 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -506,7 +506,7 @@ const char *get_register_name_32(unsigned int reg)
>   * Returns the set of feature flags that are supported and migratable by
>   * QEMU, for a given FeatureWord.
>   */
> -static uint32_t x86_cpu_get_migratable_flags(FeatureWord w)
> +static uint32_t x86_cpu_get_migratable_flags(FeatureWord w, bool is_amd)
>  {
>      FeatureWordInfo *wi = &feature_word_info[w];
>      uint32_t r = 0;
> @@ -514,12 +514,18 @@ static uint32_t x86_cpu_get_migratable_flags(FeatureWord w)
>  
>      for (i = 0; i < 32; i++) {
>          uint32_t f = 1U << i;
> +        FeatureWordInfo *effective_wi = wi;
> +
> +        if (is_amd && w == FEAT_8000_0001_EDX && f & CPUID_EXT2_AMD_ALIASES) {
> +            effective_wi = &feature_word_info[FEAT_1_EDX];
> +        }
> +
>          /* If the feature name is unknown, it is not supported by QEMU yet */
> -        if (!wi->feat_names[i]) {
> +        if (!effective_wi->feat_names[i]) {
>              continue;
>          }
>          /* Skip features known to QEMU, but explicitly marked as unmigratable */
> -        if (wi->unmigratable_flags & f) {
> +        if (effective_wi->unmigratable_flags & f) {
>              continue;
>          }
>          r |= f;

I don't think we need that complexity to fix the problem. We even
have a similar hack in kvm_arch_get_supported_cpuid() to make
sure it handles the alias bits properly. Instead of hacking those
functions to copy CPUID[1] data, it's much easier to simply copy
the alias bits in realizefn after we call
x86_cpu_filter_features(), not before.

The following (untested) fix should be sufficient:

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index ddae932..d0b5b69 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -2897,6 +2897,14 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
         env->cpuid_level = 7;
     }
 
+    if (x86_cpu_filter_features(cpu) && cpu->enforce_cpuid) {
+        error_setg(&local_err,
+                   kvm_enabled() ?
+                       "Host doesn't support requested features" :
+                       "TCG doesn't support requested features");
+        goto out;
+    }
+
     /* On AMD CPUs, some CPUID[8000_0001].EDX bits must match the bits on
      * CPUID[1].EDX.
      */
@@ -2907,14 +2915,6 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
     }
 
 
-    if (x86_cpu_filter_features(cpu) && cpu->enforce_cpuid) {
-        error_setg(&local_err,
-                   kvm_enabled() ?
-                       "Host doesn't support requested features" :
-                       "TCG doesn't support requested features");
-        goto out;
-    }
-
 #ifndef CONFIG_USER_ONLY
     qemu_register_reset(x86_cpu_machine_reset_cb, cpu);
 


-- 
Eduardo

Re: [Qemu-devel] [PATCH] target-i386: add AMD CPUID.1:edx aliases to x86_cpu_get_migratable_flags

[Radim Krčmář]

2016-04-15 13:54-0300, Eduardo Habkost:
> On Thu, Apr 14, 2016 at 10:55:07PM +0200, Radim Krčmář wrote:
>> QEMU complains about -cpu host on an AMD machine:
>>   warning: host doesn't support requested feature: CPUID.80000001H:EDX [bit 0]
>> For bits 0,1,3,4,5,6,7,8,9,12,13,14,15,16,17,23,24.
>> 
>> Host does support them, but x86_cpu_get_migratable_flags filters unnamed
>> features and drops these bits without realizing that they are aliases to
>> CPUID.1H:EDX and have their names there.
>> 
>> See https://bugzilla.redhat.com/show_bug.cgi?id=1326721 for details.
>> 
>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>> ---
>>  target-i386/cpu.c | 40 ++++++++++++++++++++++------------------
>>  1 file changed, 22 insertions(+), 18 deletions(-)
> 
> I don't think we need that complexity to fix the problem. We even
> have a similar hack in kvm_arch_get_supported_cpuid() to make
> sure it handles the alias bits properly. Instead of hacking those
> functions to copy CPUID[1] data, it's much easier to simply copy
> the alias bits in realizefn after we call
> x86_cpu_filter_features(), not before.
> 
> The following (untested) fix should be sufficient:

It is,

Tested-by: Radim Krčmář <rkrcmar@redhat.com>

Thank you.

> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index ddae932..d0b5b69 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -2897,6 +2897,14 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
>          env->cpuid_level = 7;
>      }
>  
> +    if (x86_cpu_filter_features(cpu) && cpu->enforce_cpuid) {
> +        error_setg(&local_err,
> +                   kvm_enabled() ?
> +                       "Host doesn't support requested features" :
> +                       "TCG doesn't support requested features");
> +        goto out;
> +    }
> +
>      /* On AMD CPUs, some CPUID[8000_0001].EDX bits must match the bits on
>       * CPUID[1].EDX.
>       */
> @@ -2907,14 +2915,6 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
>      }
>  
>  
> -    if (x86_cpu_filter_features(cpu) && cpu->enforce_cpuid) {
> -        error_setg(&local_err,
> -                   kvm_enabled() ?
> -                       "Host doesn't support requested features" :
> -                       "TCG doesn't support requested features");
> -        goto out;
> -    }
> -
>  #ifndef CONFIG_USER_ONLY
>      qemu_register_reset(x86_cpu_machine_reset_cb, cpu);
>  
> 
> 
> -- 
> Eduardo