Index: sys/x86/iommu/intel_drv.c
===================================================================
--- sys/x86/iommu/intel_drv.c
+++ sys/x86/iommu/intel_drv.c
@@ -405,6 +405,7 @@
 	struct dmar_unit *unit;
 	ACPI_DMAR_HARDWARE_UNIT *dmaru;
 	uint64_t timeout;
+	int disable_pmr;
 	int i, error;
 
 	unit = device_get_softc(dev);
@@ -528,6 +529,14 @@
 		dmar_release_resources(dev, unit);
 		return (error);
 	}
+	disable_pmr = 0;
+	TUNABLE_INT_FETCH("hw.dmar.pmr.disable", &disable_pmr);
+	if (disable_pmr) {
+		error = dmar_disable_protected_regions(unit);
+		if (error != 0)
+			device_printf(dev,
+			    "Failed to disable protected regions\n");
+	}
 	error = iommu_init_busdma(&unit->iommu);
 	if (error != 0) {
 		dmar_release_resources(dev, unit);
Index: sys/x86/iommu/intel_utils.c
===================================================================
--- sys/x86/iommu/intel_utils.c
+++ sys/x86/iommu/intel_utils.c
@@ -508,6 +508,9 @@
 		return (0);
 
 	reg = dmar_read4(unit, DMAR_PMEN_REG);
+	if ((reg & DMAR_PMEN_EPM) == 0)
+		return (0);
+
 	reg &= ~DMAR_PMEN_EPM;
 	dmar_write4(unit, DMAR_PMEN_REG, reg);
 	DMAR_WAIT_UNTIL(((dmar_read4(unit, DMAR_PMEN_REG) & DMAR_PMEN_PRS)