diff --git a/sys/sparc64/include/ofw_machdep.h b/sys/sparc64/include/ofw_machdep.h
index bd4c651ae167..64c7d5647929 100644
--- a/sys/sparc64/include/ofw_machdep.h
+++ b/sys/sparc64/include/ofw_machdep.h
@@ -31,7 +31,7 @@
 #include <sys/bus.h>
 
 void OF_getetheraddr(device_t dev, u_char *addr);
-
+void cpu_shutdown(void *);
 void openfirmware_exit(void *);
 
 #endif /* _MACHINE_OFW_MACHDEP_H_ */
diff --git a/sys/sparc64/sparc64/db_interface.c b/sys/sparc64/sparc64/db_interface.c
index 4322acf58c60..b6a1e2032c0e 100644
--- a/sys/sparc64/sparc64/db_interface.c
+++ b/sys/sparc64/sparc64/db_interface.c
@@ -48,6 +48,7 @@
 #include <ddb/db_sym.h>
 #include <ddb/db_variables.h>
 
+#include <machine/atomic.h>
 #include <machine/setjmp.h>
 
 static jmp_buf *db_nofault = 0;
@@ -67,14 +68,22 @@ kdb_trap(struct trapframe *tf)
 		longjmp(db_global_jmpbuf, 1);
 	flushw();
 	ddb_regs = *tf;
+	critical_enter();
 	setjmp(db_global_jmpbuf);
 	db_global_jmpbuf_valid = TRUE;
-	db_active++;
+	atomic_add_acq_int(&db_active, 1);
+#ifdef SMP
+	stop_cpus(PCPU_GET(other_cpus));
+#endif
 	cndbctl(TRUE);
 	db_trap(tf->tf_type, 0);
 	cndbctl(FALSE);
 	db_active--;
+#ifdef SMP
+	restart_cpus(stopped_cpus);
+#endif
 	db_global_jmpbuf_valid = FALSE;
+	critical_exit();
 	*tf = ddb_regs;
 	TF_DONE(tf);
 	return (1);
diff --git a/sys/sparc64/sparc64/machdep.c b/sys/sparc64/sparc64/machdep.c
index 8ac75288429c..5e96a407846b 100644
--- a/sys/sparc64/sparc64/machdep.c
+++ b/sys/sparc64/sparc64/machdep.c
@@ -525,6 +525,20 @@ sigreturn(struct thread *td, struct sigreturn_args *uap)
 	return (EJUSTRETURN);
 }
 
+/*
+ * Exit the kernel and execute a firmware call that will not return, as
+ * specified by the arguments.
+ */
+void
+cpu_shutdown(void *args)
+{
+
+#ifdef SMP
+	cpu_mp_shutdown();
+#endif
+	openfirmware_exit(args);
+}
+
 /*
  * Duplicate OF_exit() with a different firmware call function that restores
  * the trap table, otherwise a RED state exception is triggered in at least
@@ -543,7 +557,7 @@ cpu_halt(void)
 		0
 	};
 
-	openfirmware_exit(&args);
+	cpu_shutdown(&args);
 }
 
 void
@@ -561,11 +575,10 @@ sparc64_shutdown_final(void *dummy, int howto)
 
 	/* Turn the power off? */
 	if ((howto & RB_POWEROFF) != 0)
-		openfirmware_exit(&args);
+		cpu_shutdown(&args);
 	/* In case of halt, return to the firmware */
 	if ((howto & RB_HALT) != 0)
 		cpu_halt();
-		
 }
 
 int
diff --git a/sys/sparc64/sparc64/mp_machdep.c b/sys/sparc64/sparc64/mp_machdep.c
index 03f53909d1a5..1176c37d8c61 100644
--- a/sys/sparc64/sparc64/mp_machdep.c
+++ b/sys/sparc64/sparc64/mp_machdep.c
@@ -74,8 +74,12 @@
 
 #include <dev/ofw/openfirm.h>
 
+#include <ddb/ddb.h>
+
 #include <machine/asi.h>
+#include <machine/atomic.h>
 #include <machine/md_var.h>
+#include <machine/ofw_machdep.h>
 #include <machine/smp.h>
 #include <machine/tlb.h>
 #include <machine/tte.h>
@@ -91,7 +95,6 @@ static ih_func_t cpu_ipi_stop;
  */
 struct	cpu_start_args cpu_start_args = { 0, -1, -1, 0, 0 };
 struct	ipi_tlb_args ipi_tlb_args;
-struct	ipi_level_args ipi_level_args;
 
 vm_offset_t mp_tramp;
 
@@ -99,6 +102,8 @@ static struct mtx ap_boot_mtx;
 
 u_int	mp_boot_mid;
 
+static volatile u_int	shutdown_cpus;
+
 void cpu_mp_unleash(void *);
 SYSINIT(cpu_mp_unleash, SI_SUB_SMP, SI_ORDER_FIRST, cpu_mp_unleash, NULL);
 
@@ -173,6 +178,26 @@ sun4u_startcpu(phandle_t cpu, void *func, u_long arg)
 	openfirmware(&args);
 }
 
+/*
+ * Stop the calling CPU.
+ */
+static void
+sun4u_stopself(void)
+{
+	static struct {
+		cell_t	name;
+		cell_t	nargs;
+		cell_t	nreturns;
+	} args = {
+		(cell_t)"SUNW,stop-self",
+		0,
+		0,
+	};
+
+	openfirmware_exit(&args);
+	panic("sun4u_stopself: failed.");
+}
+
 /*
  * Fire up any non-boot processors.
  */
@@ -235,6 +260,7 @@ cpu_mp_start(void)
 		all_cpus |= 1 << cpuid;
 	}
 	PCPU_SET(other_cpus, all_cpus & ~(1 << PCPU_GET(cpuid)));
+	smp_active = 1;
 }
 
 void
@@ -294,6 +320,7 @@ cpu_mp_unleash(void *v)
 
 	membar(StoreLoad);
 	csa->csa_count = 0; 
+	smp_started = 1;
 }
 
 void
@@ -304,6 +331,7 @@ cpu_mp_bootstrap(struct pcpu *pc)
 	csa = &cpu_start_args;
 	pmap_map_tsb();
 	cpu_setregs(pc);
+	tick_start_ap();
 
 	smp_cpus++;
 	PCPU_SET(other_cpus, all_cpus & ~(1 << PCPU_GET(cpuid)));
@@ -323,6 +351,27 @@ cpu_mp_bootstrap(struct pcpu *pc)
 	cpu_throw();	/* doesn't return */
 }
 
+void
+cpu_mp_shutdown(void)
+{
+	int i;
+
+	critical_enter();
+	shutdown_cpus = PCPU_GET(other_cpus);
+	if (stopped_cpus != PCPU_GET(other_cpus))	/* XXX */
+		stop_cpus(stopped_cpus ^ PCPU_GET(other_cpus));
+	i = 0;
+	while (shutdown_cpus != 0) {
+		if (i++ > 100000) {
+			printf("timeout shutting down CPUs.\n");
+			break;
+		}
+	}
+	/* XXX: delay a bit to allow the CPUs to actually enter the PROM. */
+	DELAY(100000);
+	critical_exit();
+}
+
 static void
 cpu_ipi_ast(struct trapframe *tf)
 {
@@ -331,7 +380,18 @@ cpu_ipi_ast(struct trapframe *tf)
 static void
 cpu_ipi_stop(struct trapframe *tf)
 {
-	TODO;
+
+	CTR1(KTR_SMP, "cpu_ipi_stop: stopped %d", PCPU_GET(cpuid));
+	atomic_set_acq_int(&stopped_cpus, PCPU_GET(cpumask));
+	while ((started_cpus & PCPU_GET(cpumask)) == 0) {
+		if ((shutdown_cpus & PCPU_GET(cpumask)) != 0) {
+			atomic_clear_int(&shutdown_cpus, PCPU_GET(cpumask));
+			sun4u_stopself();
+		}
+	}
+	atomic_clear_rel_int(&started_cpus, PCPU_GET(cpumask));
+	atomic_clear_rel_int(&stopped_cpus, PCPU_GET(cpumask));
+	CTR1(KTR_SMP, "cpu_ipi_stop: restarted %d", PCPU_GET(cpuid));
 }
 
 void
@@ -369,7 +429,10 @@ cpu_ipi_send(u_int mid, u_long d0, u_long d1, u_long d2)
 		if ((ldxa(0, ASI_INTR_DISPATCH_STATUS) & IDR_NACK) == 0)
 			return;
 	}
-	panic("ipi_send: couldn't send ipi");
+	if (db_active || panicstr != NULL)
+		printf("ipi_send: couldn't send ipi to module %u\n", mid);
+	else
+		panic("ipi_send: couldn't send ipi");
 }
 
 void