A vcpu only checks if a rendezvous is ongoing or not to decide if it should handle a rendezvous. This could lead to spurios rendezvous where a vcpu tries a handle a rendezvous it isn't part of. This situation is properly handled by `vm_handle_rendezvous` but it could potentially degrade the performance. Avoid that by an early check if the vcpu is part of the rendezvous or not.
At the moment, rendezvous are only used to spin up application processors and to send ioapic interrupts. Spinning up application processor is done in the guest boot phase by sending INIT SIPI sequences to single vcpus. This is known to cause spurious rendezvous but only occurs in the boot phase. Sending ioapic interrupts is rare because modern guest will use msi and the rendezvous is always send to all vcpus.