--- sys/dev/cpuctl/cpuctl.c.orig	2018-03-17 00:49:59.000000000 +0100
+++ sys/dev/cpuctl/cpuctl.c	2018-03-26 22:50:33.209937000 +0200
@@ -362,6 +362,8 @@
 	is_bound = cpu_sched_is_bound(td);
 	set_cpu(cpu, td);
 	critical_enter();
+	wrmsr_safe(MSR_BIOS_SIGN, 0);
+	do_cpuid(1, tmp);
 	rdmsr_safe(MSR_BIOS_SIGN, &rev0); /* Get current microcode revision. */
 
 	/*
@@ -373,9 +375,9 @@
 	/*
 	 * Serialize instruction flow.
 	 */
-	do_cpuid(0, tmp);
-	critical_exit();
+	do_cpuid(1, tmp);
 	rdmsr_safe(MSR_BIOS_SIGN, &rev1); /* Get new microcode revision. */
+	critical_exit();
 	restore_cpu(oldcpu, is_bound, td);
 	if (rev1 > rev0)
 		ret = 0;