[PATCH 2/2] apic: Use 32bit APIC ID for migration instance ID

[Peter Xu]

Migration is silently broken now with x2apic config like this:

     -smp 200,maxcpus=288,sockets=2,cores=72,threads=2 \
     -device intel-iommu,intremap=on,eim=on

After migration, the guest kernel could hang at anything, due to
x2apic bit not migrated correctly in IA32_APIC_BASE on some vcpus, so
any operations related to x2apic could be broken then (e.g., RDMSR on
x2apic MSRs could fail because KVM would think that the vcpu hasn't
enabled x2apic at all).

The issue is that the x2apic bit was never applied correctly for vcpus
whose ID > 255 when migrate completes, and that's because when we
migrate APIC we use the APICCommonState.id as instance ID of the
migration stream, while that's too short for x2apic.

Let's use the newly introduced initial_apic_id for that.

Signed-off-by: Peter Xu <address@hidden>
---
 hw/intc/apic_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
index aafd8e0e33..6024a3e06a 100644
--- a/hw/intc/apic_common.c
+++ b/hw/intc/apic_common.c
@@ -315,7 +315,7 @@ static void apic_common_realize(DeviceState *dev, Error 
**errp)
     APICCommonState *s = APIC_COMMON(dev);
     APICCommonClass *info;
     static DeviceState *vapic;
-    int instance_id = s->id;
+    int64_t instance_id = s->initial_apic_id;
 
     info = APIC_COMMON_GET_CLASS(s);
     info->realize(dev, errp);
-- 
2.21.0