xen: credit2: properly schedule migration of a running vcpu.

If wanting to migrate a vcpu that is actually running,
we need to ask the scheduler to chime in as soon as
possible, to have the vcpu itself stopped and actually
moved.

Make sure this happens by, after setting all the relevant
flags, raising the scheduler softirq.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>

xen/common/sched_credit2.c

@@ -1667,6 +1667,7 @@ static void migrate(const struct scheduler *ops,
         svc->migrate_rqd = trqd;
         __set_bit(_VPF_migrating, &svc->vcpu->pause_flags);
         __set_bit(__CSFLAG_runq_migrate_request, &svc->flags);
+        cpu_raise_softirq(svc->vcpu->processor, SCHEDULE_SOFTIRQ);
         SCHED_STAT_CRANK(migrate_requested);
     }
     else