With CONFIG_DEBUG_PREEMPT, get_paca() produces the following warning
in kvmppc_book3s_init_hv() since it calls debug_smp_processor_id().
There is no real issue with the xics_phys field.
If paca->kvm_hstate.xics_phys is non-zero on one cpu, it will be
non-zero on them all. Therefore this is not fixing any actual
problem, just the warning.