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[PULL 28/30] apic: Use 32bit APIC ID for migration instance ID

From: Juan Quintela
Subject: [PULL 28/30] apic: Use 32bit APIC ID for migration instance ID
Date: Tue, 14 Jan 2020 12:39:24 +0100

From: Peter Xu <address@hidden>

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>
Reviewed-by: Juan Quintela <address@hidden>
Reviewed-by: Eduardo Habkost <address@hidden>
Signed-off-by: Juan Quintela <address@hidden>
 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 54b8731fca..b5dbeb6206 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 
     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);

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