spapr_cpu_core: vmstate_[un]register per-CPU data from (un)realizefn

VMStateDescription vmstate_spapr_cpu_state was added by commit
b940202 (spapr_cpu_core: migrate per-CPU data) to migrate per-CPU
data with the required vmstate registration and unregistration calls.
However the unregistration is being done only from vcpu creation error path
and not from CPU delete path.

This causes migration to fail with the following error if migration is
attempted after a CPU unplug like this:
Unknown savevm section or instance 'spapr_cpu' 16
Additionally this leaves the source VM unresponsive after migration failure.

Fix this by ensuring the vmstate_unregister happens during CPU removal.
Fixing this becomes easier when vmstate (un)registration calls are moved to
vcpu (un)realize functions which is what this patch does.

Fixes: https://bugs.launchpad.net/qemu/+bug/1785972
Reported-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr_cpu_core.c

@@ -113,26 +113,6 @@ const char *spapr_get_cpu_core_type(const char *cpu_type)
     return object_class_get_name(oc);
 }
 
-static void spapr_unrealize_vcpu(PowerPCCPU *cpu)
-{
-    qemu_unregister_reset(spapr_cpu_reset, cpu);
-    object_unparent(cpu->intc);
-    cpu_remove_sync(CPU(cpu));
-    object_unparent(OBJECT(cpu));
-}
-
-static void spapr_cpu_core_unrealize(DeviceState *dev, Error **errp)
-{
-    sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
-    CPUCore *cc = CPU_CORE(dev);
-    int i;
-
-    for (i = 0; i < cc->nr_threads; i++) {
-        spapr_unrealize_vcpu(sc->threads[i]);
-    }
-    g_free(sc->threads);
-}
-
 static bool slb_shadow_needed(void *opaque)
 {
     sPAPRCPUState *spapr_cpu = opaque;
@@ -207,10 +187,34 @@ static const VMStateDescription vmstate_spapr_cpu_state = {
     }
 };
 
+static void spapr_unrealize_vcpu(PowerPCCPU *cpu, sPAPRCPUCore *sc)
+{
+    if (!sc->pre_3_0_migration) {
+        vmstate_unregister(NULL, &vmstate_spapr_cpu_state, cpu->machine_data);
+    }
+    qemu_unregister_reset(spapr_cpu_reset, cpu);
+    object_unparent(cpu->intc);
+    cpu_remove_sync(CPU(cpu));
+    object_unparent(OBJECT(cpu));
+}
+
+static void spapr_cpu_core_unrealize(DeviceState *dev, Error **errp)
+{
+    sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
+    CPUCore *cc = CPU_CORE(dev);
+    int i;
+
+    for (i = 0; i < cc->nr_threads; i++) {
+        spapr_unrealize_vcpu(sc->threads[i], sc);
+    }
+    g_free(sc->threads);
+}
+
 static void spapr_realize_vcpu(PowerPCCPU *cpu, sPAPRMachineState *spapr,
-                               Error **errp)
+                               sPAPRCPUCore *sc, Error **errp)
 {
     CPUPPCState *env = &cpu->env;
+    CPUState *cs = CPU(cpu);
     Error *local_err = NULL;
 
     object_property_set_bool(OBJECT(cpu), true, "realized", &local_err);
@@ -233,6 +237,11 @@ static void spapr_realize_vcpu(PowerPCCPU *cpu, sPAPRMachineState *spapr,
         goto error_unregister;
     }
 
+    if (!sc->pre_3_0_migration) {
+        vmstate_register(NULL, cs->cpu_index, &vmstate_spapr_cpu_state,
+                         cpu->machine_data);
+    }
+
     return;
 
 error_unregister:
@@ -272,10 +281,6 @@ static PowerPCCPU *spapr_create_vcpu(sPAPRCPUCore *sc, int i, Error **errp)
     }
 
     cpu->machine_data = g_new0(sPAPRCPUState, 1);
-    if (!sc->pre_3_0_migration) {
-        vmstate_register(NULL, cs->cpu_index, &vmstate_spapr_cpu_state,
-                         cpu->machine_data);
-    }
 
     object_unref(obj);
     return cpu;
@@ -290,9 +295,6 @@ static void spapr_delete_vcpu(PowerPCCPU *cpu, sPAPRCPUCore *sc)
 {
     sPAPRCPUState *spapr_cpu = spapr_cpu_state(cpu);
 
-    if (!sc->pre_3_0_migration) {
-        vmstate_unregister(NULL, &vmstate_spapr_cpu_state, cpu->machine_data);
-    }
     cpu->machine_data = NULL;
     g_free(spapr_cpu);
     object_unparent(OBJECT(cpu));
@@ -325,7 +327,7 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
     }
 
     for (j = 0; j < cc->nr_threads; j++) {
-        spapr_realize_vcpu(sc->threads[j], spapr, &local_err);
+        spapr_realize_vcpu(sc->threads[j], spapr, sc, &local_err);
         if (local_err) {
             goto err_unrealize;
         }
@@ -334,7 +336,7 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
 
 err_unrealize:
     while (--j >= 0) {
-        spapr_unrealize_vcpu(sc->threads[j]);
+        spapr_unrealize_vcpu(sc->threads[j], sc);
     }
 err:
     while (--i >= 0) {