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From 0d5a09173eb75b7e56122c2aefb2646a2be58400 Mon Sep 17 00:00:00 2001
From: Peter Xu <>
Date: Fri, 31 Jan 2020 17:12:57 +0000
Subject: [PATCH 15/15] apic: Use 32bit APIC ID for migration instance ID

RH-Author: Peter Xu <>
Message-id: <>
Patchwork-id: 93628
O-Subject: [RHEL-AV-8.2.0 qemu-kvm PATCH 3/3] apic: Use 32bit APIC ID for migration instance ID
Bugzilla: 1529231
RH-Acked-by: Eduardo Habkost <>
RH-Acked-by: Juan Quintela <>
RH-Acked-by: Dr. David Alan Gilbert <>

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 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 <>
Reviewed-by: Juan Quintela <>
Reviewed-by: Eduardo Habkost <>
Signed-off-by: Juan Quintela <>
(cherry picked from commit 0ab994867c365db21e15f9503922c79234d8e40e)
Signed-off-by: Peter Xu <>
Signed-off-by: Danilo C. L. de Paula <>
 hw/intc/apic_common.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
index 54b8731..b5dbeb6 100644
--- a/hw/intc/apic_common.c
+++ b/hw/intc/apic_common.c
@@ -268,7 +268,10 @@ static void apic_common_realize(DeviceState *dev, Error **errp)
     APICCommonState *s = APIC_COMMON(dev);
     APICCommonClass *info;
     static DeviceState *vapic;
-    uint32_t instance_id = s->id;
+    uint32_t instance_id = s->initial_apic_id;
+    /* Normally initial APIC ID should be no more than hundreds */
+    assert(instance_id != VMSTATE_INSTANCE_ID_ANY);
     info = APIC_COMMON_GET_CLASS(s);
     info->realize(dev, errp);