diff --git a/hw/sysbus.c b/hw/sysbus.c
index 2e22be7b25..ea442acb50 100644
--- a/hw/sysbus.c
+++ b/hw/sysbus.c
@@ -19,6 +19,7 @@
 
 #include "sysbus.h"
 #include "monitor.h"
+#include "exec-memory.h"
 
 static void sysbus_dev_print(Monitor *mon, DeviceState *dev, int indent);
 static char *sysbus_get_fw_dev_path(DeviceState *dev);
@@ -49,11 +50,20 @@ void sysbus_mmio_map(SysBusDevice *dev, int n, target_phys_addr_t addr)
     }
     if (dev->mmio[n].addr != (target_phys_addr_t)-1) {
         /* Unregister previous mapping.  */
-        cpu_register_physical_memory(dev->mmio[n].addr, dev->mmio[n].size,
-                                     IO_MEM_UNASSIGNED);
+        if (dev->mmio[n].memory) {
+            memory_region_del_subregion(get_system_memory(),
+                                        dev->mmio[n].memory);
+        } else {
+            cpu_register_physical_memory(dev->mmio[n].addr, dev->mmio[n].size,
+                                         IO_MEM_UNASSIGNED);
+        }
     }
     dev->mmio[n].addr = addr;
-    if (dev->mmio[n].cb) {
+    if (dev->mmio[n].memory) {
+        memory_region_add_subregion(get_system_memory(),
+                                    addr,
+                                    dev->mmio[n].memory);
+    } else if (dev->mmio[n].cb) {
         dev->mmio[n].cb(dev, addr);
     } else {
         cpu_register_physical_memory(addr, dev->mmio[n].size,
@@ -107,6 +117,17 @@ void sysbus_init_mmio_cb(SysBusDevice *dev, target_phys_addr_t size,
     dev->mmio[n].cb = cb;
 }
 
+void sysbus_init_mmio_region(SysBusDevice *dev, MemoryRegion *memory)
+{
+    int n;
+
+    assert(dev->num_mmio < QDEV_MAX_MMIO);
+    n = dev->num_mmio++;
+    dev->mmio[n].addr = -1;
+    dev->mmio[n].size = memory_region_size(memory);
+    dev->mmio[n].memory = memory;
+}
+
 void sysbus_init_ioports(SysBusDevice *dev, pio_addr_t ioport, pio_addr_t size)
 {
     pio_addr_t i;
diff --git a/hw/sysbus.h b/hw/sysbus.h
index 4e8cb16d42..5f62e2da31 100644
--- a/hw/sysbus.h
+++ b/hw/sysbus.h
@@ -4,6 +4,7 @@
 /* Devices attached directly to the main system bus.  */
 
 #include "qdev.h"
+#include "memory.h"
 
 #define QDEV_MAX_MMIO 32
 #define QDEV_MAX_PIO 32
@@ -23,6 +24,7 @@ struct SysBusDevice {
         target_phys_addr_t size;
         mmio_mapfunc cb;
         ram_addr_t iofunc;
+        MemoryRegion *memory;
     } mmio[QDEV_MAX_MMIO];
     int num_pio;
     pio_addr_t pio[QDEV_MAX_PIO];
@@ -46,6 +48,7 @@ void sysbus_init_mmio(SysBusDevice *dev, target_phys_addr_t size,
                       ram_addr_t iofunc);
 void sysbus_init_mmio_cb(SysBusDevice *dev, target_phys_addr_t size,
                             mmio_mapfunc cb);
+void sysbus_init_mmio_region(SysBusDevice *dev, MemoryRegion *memory);
 void sysbus_init_irq(SysBusDevice *dev, qemu_irq *p);
 void sysbus_pass_irq(SysBusDevice *dev, SysBusDevice *target);
 void sysbus_init_ioports(SysBusDevice *dev, pio_addr_t ioport, pio_addr_t size);