diff --git a/sys/kern/subr_physmem.c b/sys/kern/subr_physmem.c
--- a/sys/kern/subr_physmem.c
+++ b/sys/kern/subr_physmem.c
@@ -40,7 +40,9 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/bus.h>
 #include <sys/kernel.h>
+#include <sys/module.h>
 #include <sys/physmem.h>
 
 #ifdef _KERNEL
@@ -49,7 +51,9 @@
 #include <vm/vm_page.h>
 #include <vm/vm_phys.h>
 #include <vm/vm_dumpset.h>
+
 #include <machine/md_var.h>
+#include <machine/resource.h>
 #else
 #include <stdarg.h>
 #include <stdio.h>
@@ -524,7 +528,6 @@
 		panic("No memory entries in phys_avail");
 	Maxmem = atop(phys_avail[nextidx - 1]);
 }
-#endif
 
 #ifdef DDB
 #include <ddb/ddb.h>
@@ -536,3 +539,98 @@
 }
 
 #endif /* DDB */
+
+/*
+ * ram pseudo driver - this reserves I/O space resources corresponding to physical
+ * memory regions.
+ */
+
+static void
+ram_identify(driver_t *driver, device_t parent)
+{
+
+	if (resource_disabled("ram", 0))
+		return;
+	if (BUS_ADD_CHILD(parent, 0, "ram", 0) == NULL)
+		panic("ram_identify");
+}
+
+static int
+ram_probe(device_t dev)
+{
+
+	device_quiet(dev);
+	device_set_desc(dev, "System RAM");
+	return (BUS_PROBE_SPECIFIC);
+}
+
+static int
+ram_attach(device_t dev)
+{
+	vm_paddr_t avail_list[PHYS_AVAIL_COUNT];
+	rman_res_t start, end;
+	struct region *hwp;
+	int rid, i;
+
+	rid = 0;
+
+	/* Get the avail list. */
+	bzero(avail_list, sizeof(avail_list));
+	regions_to_avail(avail_list, EXFLAG_NOALLOC | EXFLAG_NODUMP,
+	    PHYS_AVAIL_COUNT, 0, NULL, NULL);
+
+	/* Reserve all memory regions. */
+	for (i = 0; avail_list[i + 1] != 0; i += 2) {
+		start = avail_list[i];
+		end = avail_list[i + 1];
+
+		if (bootverbose)
+			device_printf(dev,
+			    "reserving memory region:   %jx-%jx\n",
+			    (uintmax_t)start, (uintmax_t)end);
+
+		if (bus_alloc_resource(dev, SYS_RES_MEMORY, &rid, start, end,
+		    end - start, 0) == NULL)
+			panic("ram_attach: resource %d failed to attach", rid);
+		rid++;
+	}
+
+	/* Now, reserve the excluded memory regions. */
+	for (i = 0, hwp = exregions; i < excnt; i++, hwp++) {
+		start = hwp->addr;
+		end = hwp->addr + hwp->size;
+
+		if (bootverbose)
+			device_printf(dev,
+			    "reserving excluded region: %jx-%jx\n",
+			    (uintmax_t)start, (uintmax_t)(end - 1));
+
+		/*
+		 * Best-effort attempt to reserve the range. This may fail, as
+		 * sometimes the excluded ranges provided by the device tree
+		 * will cover or overlap some I/O range.
+		 */
+		if (bus_alloc_resource(dev, SYS_RES_MEMORY, &rid, start, end,
+		    end - start, 0) == NULL) {
+			if (bootverbose)
+				device_printf(dev, "failed to reserve region\n");
+			continue;
+		}
+		rid++;
+	}
+
+	return (0);
+}
+
+static device_method_t ram_methods[] = {
+	/* Device interface */
+	DEVMETHOD(device_identify,	ram_identify),
+	DEVMETHOD(device_probe,		ram_probe),
+	DEVMETHOD(device_attach,	ram_attach),
+
+	DEVMETHOD_END
+};
+
+DEFINE_CLASS_0(ram, ram_driver, ram_methods, /* no softc */ 1);
+DRIVER_MODULE(ram, nexus, ram_driver, 0, 0);
+#endif /* _KERNEL */