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

[Juan Quintela <quintela@redhat.com>]

Peter Xu <peterx@redhat.com> wrote:
> 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 <peterx@redhat.com>
> ---
>  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;

int is ok here.

But damn thing, initial_apic_id is uint32_t.  Sniff.

Later, Juan.