diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 449f86897db3..240def438dc3 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -75,8 +75,14 @@ static void __cpuinit cpu_bringup(void)
 
 	xen_setup_cpu_clockevents();
 
+	notify_cpu_starting(cpu);
+
+	ipi_call_lock();
 	set_cpu_online(cpu, true);
+	ipi_call_unlock();
+
 	this_cpu_write(cpu_state, CPU_ONLINE);
+
 	wmb();
 
 	/* We can take interrupts now: we're officially "up". */