diff --git a/sys/x86/cpufreq/hwpstate_amd.c b/sys/x86/cpufreq/hwpstate_amd.c
--- a/sys/x86/cpufreq/hwpstate_amd.c
+++ b/sys/x86/cpufreq/hwpstate_amd.c
@@ -123,6 +123,7 @@
 static int	hwpstate_features(driver_t *driver, u_int *features);
 static int	hwpstate_get_info_from_acpi_perf(device_t dev, device_t perf_dev);
 static int	hwpstate_get_info_from_msr(device_t dev);
+static void	hwpstate_override_msr(device_t dev);
 static int	hwpstate_goto_pstate(device_t dev, int pstate_id);
 
 static int	hwpstate_verbose;
@@ -144,6 +145,11 @@
     &hwpstate_prefer_msr, 0,
     "If enabled (1), use MSR instead of acpi_perf for P-state information.");
 
+static char 	hwpstate_override_pstatecfgmsr[8 * sizeof("0x8000000049120890")];
+SYSCTL_STRING(_debug, OID_AUTO, hwpstate_override_pstatecfgmsr, CTLFLAG_RWTUN,
+    hwpstate_override_pstatecfgmsr, sizeof(hwpstate_override_pstatecfgmsr),
+    "Allows overriding PStateDef, up to 8 hexadecimals.");
+
 static device_method_t hwpstate_methods[] = {
 	/* Device interface */
 	DEVMETHOD(device_identify,	hwpstate_identify),
@@ -413,6 +419,9 @@
 		}
 	}
 
+	if (strlen(&hwpstate_override_pstatecfgmsr[0]) > 0)
+		hwpstate_override_msr(dev);
+
 	/*
 	 * If we cannot get info from acpi_perf,
 	 * Let's get info from MSRs.
@@ -433,6 +442,33 @@
 	return (cpufreq_register(dev));
 }
 
+static void
+hwpstate_override_msr(device_t dev)
+{
+	char temp[sizeof(hwpstate_override_pstatecfgmsr)];
+	char *token, *next;
+	uint64_t msr;
+	int i;
+
+	memcpy(&temp[0], &hwpstate_override_pstatecfgmsr[0], sizeof(temp));
+	next = &temp[0];
+	token = strsep(&next, " ");
+	/* Ignore PStateCurLim here, sysadmin knows best. */
+	for (i = 0; (i < 8) && (token != NULL); ++i) {
+		if (sscanf(token, "0x%lx", &msr) == 1) {
+			HWPSTATE_DEBUG(dev, "Overriding P%d-state with 0x%lx.\n",
+			    i, msr);
+			wrmsr(MSR_AMD_10H_11H_CONFIG + i, msr);
+		} else {
+			HWPSTATE_DEBUG(dev,
+			    "P%d-state MSR override value not parsable: \"%s\"\n",
+			    i, token);
+			break;
+		}
+		token = strsep(&next, " ");
+	}
+}
+
 static int
 hwpstate_get_info_from_msr(device_t dev)
 {
@@ -449,6 +485,7 @@
 	hwpstate_set = sc->hwpstate_settings;
 	for (i = 0; i < sc->cfnum; i++) {
 		msr = rdmsr(MSR_AMD_10H_11H_CONFIG + i);
+		HWPSTATE_DEBUG(dev, "PStateDef[%d]: 0x%lx\n", i, msr);
 		if ((msr & ((uint64_t)1 << 63)) == 0) {
 			HWPSTATE_DEBUG(dev, "msr is not valid.\n");
 			return (ENXIO);