[RFC PATCH] target/i386: Set family/model/stepping of the "max" CPU according to LM bit

[RFC PATCH] target/i386: Set family/model/stepping of the "max" CPU according to LM bit

[Thomas Huth]

We want to get rid of the "#ifdef TARGET_X86_64" compile-time switch
in the long run, so we can drop the separate compilation of the
"qemu-system-i386" binary one day - but we then still need a way to
run a guest with max. CPU settings in 32-bit mode. So the "max" CPU
should determine its family/model/stepping settings according to the
"large mode" (LM) CPU feature bit during runtime, so that it is
possible to run "qemu-system-x86_64 -cpu max,lm=off" and still get
a sane family/model/stepping setting for the guest CPU.

To be able to check the LM bit, we have to move the code that sets
up these properties to a "realize" function, since the LM setting is
not available yet when the "instance_init" function is being called.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 target/i386/cpu.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index cab1e2a957..fe3b78fc95 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -44,6 +44,8 @@
 #include "disas/capstone.h"
 #include "cpu-internal.h"
 
+static void x86_cpu_realizefn(DeviceState *dev, Error **errp);
+
 /* Helpers for building CPUID[2] descriptors: */
 
 struct CPUID2CacheDescriptorInfo {
@@ -4315,6 +4317,25 @@ static Property max_x86_cpu_properties[] = {
     DEFINE_PROP_END_OF_LIST()
 };
 
+static void max_x86_cpu_realize(DeviceState *dev, Error **errp)
+{
+    Object *obj = OBJECT(dev);
+
+    if (!object_property_get_int(obj, "family", &error_abort)) {
+        if (X86_CPU(obj)->env.features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) {
+            object_property_set_int(obj, "family", 15, &error_abort);
+            object_property_set_int(obj, "model", 107, &error_abort);
+            object_property_set_int(obj, "stepping", 1, &error_abort);
+        } else {
+            object_property_set_int(obj, "family", 6, &error_abort);
+            object_property_set_int(obj, "model", 6, &error_abort);
+            object_property_set_int(obj, "stepping", 3, &error_abort);
+        }
+    }
+
+    x86_cpu_realizefn(dev, errp);
+}
+
 static void max_x86_cpu_class_init(ObjectClass *oc, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(oc);
@@ -4326,6 +4347,7 @@ static void max_x86_cpu_class_init(ObjectClass *oc, void *data)
         "Enables all features supported by the accelerator in the current host";
 
     device_class_set_props(dc, max_x86_cpu_properties);
+    dc->realize = max_x86_cpu_realize;
 }
 
 static void max_x86_cpu_initfn(Object *obj)
@@ -4344,15 +4366,6 @@ static void max_x86_cpu_initfn(Object *obj)
      */
     object_property_set_str(OBJECT(cpu), "vendor", CPUID_VENDOR_AMD,
                             &error_abort);
-#ifdef TARGET_X86_64
-    object_property_set_int(OBJECT(cpu), "family", 15, &error_abort);
-    object_property_set_int(OBJECT(cpu), "model", 107, &error_abort);
-    object_property_set_int(OBJECT(cpu), "stepping", 1, &error_abort);
-#else
-    object_property_set_int(OBJECT(cpu), "family", 6, &error_abort);
-    object_property_set_int(OBJECT(cpu), "model", 6, &error_abort);
-    object_property_set_int(OBJECT(cpu), "stepping", 3, &error_abort);
-#endif
     object_property_set_str(OBJECT(cpu), "model-id",
                             "QEMU TCG CPU version " QEMU_HW_VERSION,
                             &error_abort);
-- 
2.31.1

Re: [RFC PATCH] target/i386: Set family/model/stepping of the "max" CPU according to LM bit

[Daniel P. Berrangé]

On Mon, Mar 06, 2023 at 04:43:11PM +0100, Thomas Huth wrote:
> We want to get rid of the "#ifdef TARGET_X86_64" compile-time switch
> in the long run, so we can drop the separate compilation of the
> "qemu-system-i386" binary one day - but we then still need a way to
> run a guest with max. CPU settings in 32-bit mode. So the "max" CPU
> should determine its family/model/stepping settings according to the
> "large mode" (LM) CPU feature bit during runtime, so that it is
> possible to run "qemu-system-x86_64 -cpu max,lm=off" and still get
> a sane family/model/stepping setting for the guest CPU.
> 
> To be able to check the LM bit, we have to move the code that sets
> up these properties to a "realize" function, since the LM setting is
> not available yet when the "instance_init" function is being called.

Ah, yes, makes sense.

> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  target/i386/cpu.c | 31 ++++++++++++++++++++++---------
>  1 file changed, 22 insertions(+), 9 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index cab1e2a957..fe3b78fc95 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -44,6 +44,8 @@
>  #include "disas/capstone.h"
>  #include "cpu-internal.h"
>  
> +static void x86_cpu_realizefn(DeviceState *dev, Error **errp);
> +
>  /* Helpers for building CPUID[2] descriptors: */
>  
>  struct CPUID2CacheDescriptorInfo {
> @@ -4315,6 +4317,25 @@ static Property max_x86_cpu_properties[] = {
>      DEFINE_PROP_END_OF_LIST()
>  };
>  
> +static void max_x86_cpu_realize(DeviceState *dev, Error **errp)
> +{
> +    Object *obj = OBJECT(dev);
> +
> +    if (!object_property_get_int(obj, "family", &error_abort)) {
> +        if (X86_CPU(obj)->env.features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) {
> +            object_property_set_int(obj, "family", 15, &error_abort);
> +            object_property_set_int(obj, "model", 107, &error_abort);
> +            object_property_set_int(obj, "stepping", 1, &error_abort);
> +        } else {
> +            object_property_set_int(obj, "family", 6, &error_abort);
> +            object_property_set_int(obj, "model", 6, &error_abort);
> +            object_property_set_int(obj, "stepping", 3, &error_abort);
> +        }
> +    }
> +
> +    x86_cpu_realizefn(dev, errp);
> +}
> +
>  static void max_x86_cpu_class_init(ObjectClass *oc, void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(oc);
> @@ -4326,6 +4347,7 @@ static void max_x86_cpu_class_init(ObjectClass *oc, void *data)
>          "Enables all features supported by the accelerator in the current host";
>  
>      device_class_set_props(dc, max_x86_cpu_properties);
> +    dc->realize = max_x86_cpu_realize;
>  }
>  
>  static void max_x86_cpu_initfn(Object *obj)
> @@ -4344,15 +4366,6 @@ static void max_x86_cpu_initfn(Object *obj)
>       */
>      object_property_set_str(OBJECT(cpu), "vendor", CPUID_VENDOR_AMD,
>                              &error_abort);
> -#ifdef TARGET_X86_64
> -    object_property_set_int(OBJECT(cpu), "family", 15, &error_abort);
> -    object_property_set_int(OBJECT(cpu), "model", 107, &error_abort);
> -    object_property_set_int(OBJECT(cpu), "stepping", 1, &error_abort);
> -#else
> -    object_property_set_int(OBJECT(cpu), "family", 6, &error_abort);
> -    object_property_set_int(OBJECT(cpu), "model", 6, &error_abort);
> -    object_property_set_int(OBJECT(cpu), "stepping", 3, &error_abort);
> -#endif
>      object_property_set_str(OBJECT(cpu), "model-id",
>                              "QEMU TCG CPU version " QEMU_HW_VERSION,
>                              &error_abort);
> -- 
> 2.31.1
> 

With regards,
Daniel
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