[Qemu-devel] [PATCH v3 15/19] apic: use apic_id as apic's migration instance_id

[Igor Mammedov <imammedo@redhat.com>]

instance_id is generated by last_used_id + 1 for a given device type
so for QEMU with 3 CPUs instance_id for APICs is a seti of [0, 1, 2]
When CPU in the middle is hot-removed and migration started
APICs with instance_ids 0 and 2 are transferred in migration stream.
However target starts with 2 CPUs and APICs' instance_ids are
generated from scratch [0, 1] hence migration fails with error
  Unknown savevm section or instance 'apic' 2

Fix issue by manually registering APIC's vmsd with apic_id as
instance_id, in this case instance_id on target will always
match instance_id on source as apic_id is the same for a given
cpu instance.

Reported-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 hw/intc/apic_common.c           | 12 +++++++++++-
 include/hw/i386/apic_internal.h |  1 +
 include/hw/i386/pc.h            |  5 +++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
index 0bb9ad5..14ac43c 100644
--- a/hw/intc/apic_common.c
+++ b/hw/intc/apic_common.c
@@ -294,11 +294,14 @@ static int apic_load_old(QEMUFile *f, void *opaque, int version_id)
     return 0;
 }
 
+static const VMStateDescription vmstate_apic_common;
+
 static void apic_common_realize(DeviceState *dev, Error **errp)
 {
     APICCommonState *s = APIC_COMMON(dev);
     APICCommonClass *info;
     static DeviceState *vapic;
+    int instance_id = s->id;
 
     info = APIC_COMMON_GET_CLASS(s);
     info->realize(dev, errp);
@@ -313,6 +316,11 @@ static void apic_common_realize(DeviceState *dev, Error **errp)
         info->enable_tpr_reporting(s, true);
     }
 
+    if (s->legacy_instance_id) {
+        instance_id = -1;
+    }
+    vmstate_register_with_alias_id(NULL, instance_id, &vmstate_apic_common,
+                                   s, -1, 0);
 }
 
 static void apic_common_unrealize(DeviceState *dev, Error **errp)
@@ -320,6 +328,7 @@ static void apic_common_unrealize(DeviceState *dev, Error **errp)
     APICCommonState *s = APIC_COMMON(dev);
     APICCommonClass *info = APIC_COMMON_GET_CLASS(s);
 
+    vmstate_unregister(NULL, &vmstate_apic_common, s);
     info->unrealize(dev, errp);
 
     if (apic_report_tpr_access && info->enable_tpr_reporting) {
@@ -422,6 +431,8 @@ static Property apic_properties_common[] = {
     DEFINE_PROP_UINT8("version", APICCommonState, version, 0x14),
     DEFINE_PROP_BIT("vapic", APICCommonState, vapic_control, VAPIC_ENABLE_BIT,
                     true),
+    DEFINE_PROP_BOOL("legacy-instance-id", APICCommonState, legacy_instance_id,
+                     false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -429,7 +440,6 @@ static void apic_common_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
 
-    dc->vmsd = &vmstate_apic_common;
     dc->reset = apic_reset_common;
     dc->props = apic_properties_common;
     dc->realize = apic_common_realize;
diff --git a/include/hw/i386/apic_internal.h b/include/hw/i386/apic_internal.h
index 52ca45d..a694322 100644
--- a/include/hw/i386/apic_internal.h
+++ b/include/hw/i386/apic_internal.h
@@ -182,6 +182,7 @@ struct APICCommonState {
     uint32_t vapic_control;
     DeviceState *vapic;
     hwaddr vapic_paddr; /* note: persistence via kvmvapic */
+    bool legacy_instance_id;
 };
 
 typedef struct VAPICState {
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 7e43b20..e2f0426 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -374,6 +374,11 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .driver   = TYPE_X86_CPU,\
         .property = "cpuid-0xb",\
         .value    = "off",\
+    },\
+    {\
+        .driver   = "apic",\
+        .property = "legacy-instance-id",\
+        .value    = "on",\
     },
 
 #define PC_COMPAT_2_5 \
-- 
2.7.0