[Qemu-devel] [RFC PATCH v2 2/5] cpu: Introduce CPUState::stable_cpu_id

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

Add CPUState::stable_cpu_id and use that as instance_id in
vmstate_register() call.

Introduce has-stable_cpu_id property that allows target machines to
optionally switch to using stable_cpu_id instead of cpu_index.
This will help allow successful migration in cases where holes are
introduced in cpu_index range after CPU hot removals.

Suggested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
---
 exec.c            | 6 ++++--
 include/qom/cpu.h | 5 +++++
 qom/cpu.c         | 6 ++++++
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/exec.c b/exec.c
index fb73910..3b36fe5 100644
--- a/exec.c
+++ b/exec.c
@@ -619,12 +619,14 @@ static void cpu_release_index(CPUState *cpu)
 void cpu_vmstate_register(CPUState *cpu)
 {
     CPUClass *cc = CPU_GET_CLASS(cpu);
+    int instance_id = cpu->has_stable_cpu_id ? cpu->stable_cpu_id :
+                      cpu->cpu_index;
 
     if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
-        vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
+        vmstate_register(NULL, instance_id, &vmstate_cpu_common, cpu);
     }
     if (cc->vmsd != NULL) {
-        vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
+        vmstate_register(NULL, instance_id, cc->vmsd, cpu);
     }
 }
 
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 331386f..527c021 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -273,6 +273,9 @@ struct qemu_work_item {
  * @kvm_fd: vCPU file descriptor for KVM.
  * @work_mutex: Lock to prevent multiple access to queued_work_*.
  * @queued_work_first: First asynchronous work pending.
+ * @stable_cpu_id: Use as instance_id argument in cpu vmstate_register calls
+ * @has_stable_cpu_id: Set to enforce the use of @stable_cpu_id
+ *     over cpu_index during vmstate registration.
  *
  * State of one CPU core or thread.
  */
@@ -360,6 +363,8 @@ struct CPUState {
        (absolute value) offset as small as possible.  This reduces code
        size, especially for hosts without large memory offsets.  */
     uint32_t tcg_exit_req;
+    int stable_cpu_id;
+    bool has_stable_cpu_id;
 };
 
 QTAILQ_HEAD(CPUTailQ, CPUState);
diff --git a/qom/cpu.c b/qom/cpu.c
index 1095ea1..bae1bf7 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -363,6 +363,11 @@ static int64_t cpu_common_get_arch_id(CPUState *cpu)
     return cpu->cpu_index;
 }
 
+static Property cpu_common_properties[] = {
+    DEFINE_PROP_BOOL("has-stable-cpu-id", CPUState, has_stable_cpu_id, false),
+    DEFINE_PROP_END_OF_LIST()
+};
+
 static void cpu_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -394,6 +399,7 @@ static void cpu_class_init(ObjectClass *klass, void *data)
      * IRQs, adding reset handlers, halting non-first CPUs, ...
      */
     dc->cannot_instantiate_with_device_add_yet = true;
+    dc->props = cpu_common_properties;
 }
 
 static const TypeInfo cpu_type_info = {
-- 
2.7.4