cpu: Register VMStateDescription through CPUState

In comparison to DeviceClass::vmsd, CPU VMState is split in two,
"cpu_common" and "cpu", and uses cpu_index as instance_id instead of -1.
Therefore add a CPU-specific CPUClass::vmsd field.

Unlike the legacy CPUArchState registration, rather register CPUState.
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>

exec.c

@@ -219,7 +219,7 @@ void cpu_exec_init_all(void)
 #endif
 }
 
-#if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
+#if !defined(CONFIG_USER_ONLY)
 
 static int cpu_common_post_load(void *opaque, int version_id)
 {
@@ -245,6 +245,8 @@ static const VMStateDescription vmstate_cpu_common = {
         VMSTATE_END_OF_LIST()
     }
 };
+#else
+#define vmstate_cpu_common vmstate_dummy
 #endif
 
 CPUState *qemu_get_cpu(int index)
@@ -266,6 +268,7 @@ CPUState *qemu_get_cpu(int index)
 void cpu_exec_init(CPUArchState *env)
 {
     CPUState *cpu = ENV_GET_CPU(env);
+    CPUClass *cc = CPU_GET_CLASS(cpu);
     CPUArchState **penv;
     int cpu_index;
 
@@ -290,11 +293,15 @@ void cpu_exec_init(CPUArchState *env)
 #if defined(CONFIG_USER_ONLY)
     cpu_list_unlock();
 #endif
-#if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
     vmstate_register(NULL, cpu_index, &vmstate_cpu_common, env);
+#if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
     register_savevm(NULL, "cpu", cpu_index, CPU_SAVE_VERSION,
                     cpu_save, cpu_load, env);
+    assert(cc->vmsd == NULL);
 #endif
+    if (cc->vmsd != NULL) {
+        vmstate_register(NULL, cpu_index, cc->vmsd, cpu);
+    }
 }
 
 #if defined(TARGET_HAS_ICE)

include/qom/cpu.h

@@ -44,6 +44,7 @@ typedef struct CPUState CPUState;
  * @class_by_name: Callback to map -cpu command line model name to an
  * instantiatable CPU type.
  * @reset: Callback to reset the #CPUState to its initial state.
+ * @vmsd: State description for migration.
  *
  * Represents a CPU family or model.
  */
@@ -55,6 +56,8 @@ typedef struct CPUClass {
     ObjectClass *(*class_by_name)(const char *cpu_model);
 
     void (*reset)(CPUState *cpu);
+
+    const struct VMStateDescription *vmsd;
 } CPUClass;
 
 struct KVMState;