Index: sys/arch/arm/arm/cpu_subr.c
===================================================================
RCS file: /cvsroot/src/sys/arch/arm/arm/cpu_subr.c,v
retrieving revision 1.1
diff -u -p -r1.1 cpu_subr.c
--- sys/arch/arm/arm/cpu_subr.c	15 Feb 2020 08:16:10 -0000	1.1
+++ sys/arch/arm/arm/cpu_subr.c	30 Nov 2020 16:57:11 -0000
@@ -86,7 +86,8 @@ cpu_boot_secondary_processors(void)
 	for (size_t n = 0; n < __arraycount(arm_cpu_mbox); n++)
 		atomic_or_ulong(&arm_cpu_mbox[n], arm_cpu_hatched[n]);
 
-	__asm __volatile ("sev; sev; sev");
+	dsb(ishst);
+	__asm __volatile ("sev");
 
 	/* wait all cpus have done cpu_hatch() */
 	for (cpuno = 1; cpuno < ncpu; cpuno++) {
@@ -97,7 +98,7 @@ cpu_boot_secondary_processors(void)
 		const u_long bit = __BIT(cpuno % CPUINDEX_DIVISOR);
 
 		while (membar_consumer(), arm_cpu_mbox[off] & bit) {
-			__asm __volatile ("wfe");
+			__asm __volatile ("wfe" ::: "memory");
 		}
 		/* Add processor to kcpuset */
 		kcpuset_set(kcpuset_attached, cpuno);
@@ -136,7 +137,8 @@ cpu_clr_mbox(int cpuindex)
 	/* Notify cpu_boot_secondary_processors that we're done */
 	atomic_and_ulong(&arm_cpu_mbox[off], ~bit);
 	membar_producer();
-	__asm __volatile("sev; sev; sev");
+	dsb(ishst);
+	__asm __volatile("sev");
 }
 
 #endif