Re: [PATCH v2 3/4] apic: Use 32bit APIC ID for migration instance ID

[Eduardo Habkost]

On Wed, Oct 16, 2019 at 10:29:32AM +0800, Peter Xu 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 <address@hidden>

Reviewed-by: Eduardo Habkost <address@hidden>

-- 
Eduardo