Index: head/sys/arm64/arm64/mp_machdep.c
===================================================================
--- head/sys/arm64/arm64/mp_machdep.c
+++ head/sys/arm64/arm64/mp_machdep.c
@@ -352,7 +352,6 @@
 	if (id == 0)
 		return (1);
 
-	CPU_SET(id, &all_cpus);
 
 	pcpup = &__pcpu[id];
 	pcpu_init(pcpup, id, sizeof(struct pcpu));
@@ -371,8 +370,17 @@
 	pa = pmap_extract(kernel_pmap, (vm_offset_t)mpentry);
 
 	err = psci_cpu_on(target_cpu, pa, id);
-	if (err != PSCI_RETVAL_SUCCESS)
-		printf("Failed to start CPU %u\n", id);
+	if (err != PSCI_RETVAL_SUCCESS) {
+		/* Panic here if INVARIANTS are enabled */
+		KASSERT(0, ("Failed to start CPU %u (%lx)\n", id, target_cpu));
+
+		pcpu_destroy(pcpup);
+		kmem_free(kernel_arena, (vm_offset_t)dpcpu[id - 1], DPCPU_SIZE);
+		dpcpu[id - 1] = NULL;
+		/* Notify the user that the CPU failed to start */
+		printf("Failed to start CPU %u (%lx)\n", id, target_cpu);
+	} else
+		CPU_SET(id, &all_cpus);
 
 	return (1);
 }