Index: sys/dev/cpuctl/cpuctl.c
===================================================================
--- sys/dev/cpuctl/cpuctl.c
+++ sys/dev/cpuctl/cpuctl.c
@@ -73,6 +73,7 @@
     struct thread *td);
 static int cpuctl_do_cpuid_count(int cpu, cpuctl_cpuid_count_args_t *data,
     struct thread *td);
+static int cpuctl_do_eval_cpu_features(int cpu, struct thread *td);
 static int cpuctl_do_update(int cpu, cpuctl_update_args_t *data,
     struct thread *td);
 static int update_intel(int cpu, cpuctl_update_args_t *args,
@@ -159,7 +160,8 @@
 	}
 	/* Require write flag for "write" requests. */
 	if ((cmd == CPUCTL_MSRCBIT || cmd == CPUCTL_MSRSBIT ||
-	    cmd == CPUCTL_UPDATE || cmd == CPUCTL_WRMSR) &&
+	    cmd == CPUCTL_UPDATE || cmd == CPUCTL_WRMSR ||
+	    cmd == CPUCTL_EVAL_CPU_FEATURES) &&
 	    (flags & FWRITE) == 0)
 		return (EPERM);
 	switch (cmd) {
@@ -187,6 +189,9 @@
 		ret = cpuctl_do_cpuid_count(cpu,
 		    (cpuctl_cpuid_count_args_t *)data, td);
 		break;
+	case CPUCTL_EVAL_CPU_FEATURES:
+		ret = cpuctl_do_eval_cpu_features(cpu, td);
+		break;
 	default:
 		ret = EINVAL;
 		break;
@@ -504,6 +509,29 @@
 	return (ret);
 }
 
+static int
+cpuctl_do_eval_cpu_features(int cpu, struct thread *td)
+{
+	int is_bound = 0;
+	int oldcpu;
+
+	KASSERT(cpu >= 0 && cpu <= mp_maxid,
+	    ("[cpuctl,%d]: bad cpu number %d", __LINE__, cpu));
+
+#ifdef __i386__
+	if (cpu_id == 0)
+		return (ENODEV);
+#endif
+	oldcpu = td->td_oncpu;
+	is_bound = cpu_sched_is_bound(td);
+	set_cpu(cpu, td);
+	identify_cpu1();
+	identify_cpu2();
+	restore_cpu(oldcpu, is_bound, td);
+	return (0);
+}
+
+
 int
 cpuctl_open(struct cdev *dev, int flags, int fmt __unused, struct thread *td)
 {
Index: sys/sys/cpuctl.h
===================================================================
--- sys/sys/cpuctl.h
+++ sys/sys/cpuctl.h
@@ -59,5 +59,6 @@
 #define	CPUCTL_MSRSBIT	_IOWR('c', 5, cpuctl_msr_args_t)
 #define	CPUCTL_MSRCBIT	_IOWR('c', 6, cpuctl_msr_args_t)
 #define	CPUCTL_CPUID_COUNT _IOWR('c', 7, cpuctl_cpuid_count_args_t)
+#define	CPUCTL_EVAL_CPU_FEATURES	_IO('c', 8)
 
 #endif /* _CPUCTL_H_ */
Index: usr.sbin/cpucontrol/cpucontrol.8
===================================================================
--- usr.sbin/cpucontrol/cpucontrol.8
+++ usr.sbin/cpucontrol/cpucontrol.8
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 30, 2017
+.Dd January 2, 2018
 .Dt CPUCONTROL 8
 .Os
 .Sh NAME
@@ -76,6 +76,10 @@
 .Bk
 .Ar device
 .Ek
+.Nm
+.Fl e
+.Bk
+.Ar device
 .Sh DESCRIPTION
 The
 .Nm
@@ -136,6 +140,20 @@
 .Nm
 utility will walk through the configured data directories
 and apply all firmware updates available for this CPU.
+.It Fl e
+Re-evaluate the kernel flags indicating the present CPU features.
+This command is typically executed after a firmware update was applied
+which changes information reported by the
+.Dv CPUID
+instruction.
+.Pp
+.Bf -symbolic
+Only execute the
+.Fl e
+command after the microcode update was applied to all CPUs in the system.
+Kernel does not operate correctly if the features of processors are
+not identical.
+.Ef
 .It Fl v
 Increase the verbosity level.
 .It Fl h
Index: usr.sbin/cpucontrol/cpucontrol.c
===================================================================
--- usr.sbin/cpucontrol/cpucontrol.c
+++ usr.sbin/cpucontrol/cpucontrol.c
@@ -63,6 +63,7 @@
 #define	FLAG_M	0x02
 #define	FLAG_U	0x04
 #define	FLAG_N	0x08
+#define	FLAG_E	0x10
 
 #define	OP_INVAL	0x00
 #define	OP_READ		0x01
@@ -117,7 +118,7 @@
 	if (name == NULL)
 		name = "cpuctl";
 	fprintf(stderr, "Usage: %s [-vh] [-d datadir] [-m msr[=value] | "
-	    "-i level | -i level,level_type | -u] device\n", name);
+	    "-i level | -i level,level_type | -e | -u] device\n", name);
 	exit(EX_USAGE);
 }
 
@@ -340,6 +341,25 @@
 	return (0);
 }
 
+static int
+do_eval_cpu_features(const char *dev)
+{
+	int fd, error;
+
+	assert(dev != NULL);
+
+	fd = open(dev, O_RDWR);
+	if (fd < 0) {
+		WARN(0, "error opening %s for reading", dev);
+		return (1);
+	}
+	error = ioctl(fd, CPUCTL_EVAL_CPU_FEATURES, NULL);
+	if (error < 0)
+		WARN(0, "ioctl(%s, CPUCTL_EVAL_CPU_FEATURES)", dev);
+	close(fd);
+	return (error);
+}
+
 static int
 do_update(const char *dev)
 {
@@ -430,11 +450,14 @@
 	error = 0;
 	cmdarg = "";	/* To keep gcc3 happy. */
 
-	while ((c = getopt(argc, argv, "d:hi:m:nuv")) != -1) {
+	while ((c = getopt(argc, argv, "d:ehi:m:nuv")) != -1) {
 		switch (c) {
 		case 'd':
 			datadir_add(optarg);
 			break;
+		case 'e':
+			flags |= FLAG_E;
+			break;
 		case 'i':
 			flags |= FLAG_I;
 			cmdarg = optarg;
@@ -468,22 +491,25 @@
 	if ((flags & FLAG_N) == 0)
 		datadir_add(DEFAULT_DATADIR);
 	dev = argv[0];
-	c = flags & (FLAG_I | FLAG_M | FLAG_U);
+	c = flags & (FLAG_E | FLAG_I | FLAG_M | FLAG_U);
 	switch (c) {
-		case FLAG_I:
-			if (strstr(cmdarg, ",") != NULL)
-				error = do_cpuid_count(cmdarg, dev);
-			else
-				error = do_cpuid(cmdarg, dev);
-			break;
-		case FLAG_M:
-			error = do_msr(cmdarg, dev);
-			break;
-		case FLAG_U:
-			error = do_update(dev);
-			break;
-		default:
-			usage();	/* Only one command can be selected. */
+	case FLAG_I:
+		if (strstr(cmdarg, ",") != NULL)
+			error = do_cpuid_count(cmdarg, dev);
+		else
+			error = do_cpuid(cmdarg, dev);
+		break;
+	case FLAG_M:
+		error = do_msr(cmdarg, dev);
+		break;
+	case FLAG_U:
+		error = do_update(dev);
+		break;
+	case FLAG_E:
+		error = do_eval_cpu_features(dev);
+		break;
+	default:
+		usage();	/* Only one command can be selected. */
 	}
 	SLIST_FREE(&datadirs, next, free);
 	return (error == 0 ? 0 : 1);