diff --git a/hw/pci.c b/hw/pci.c
index ef7607e177..e80599f058 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -1066,6 +1066,26 @@ static void pci_set_irq(void *opaque, int irq_num, int level)
     pci_change_irq_level(pci_dev, irq_num, change);
 }
 
+/* Special hooks used by device assignment */
+void pci_bus_set_route_irq_fn(PCIBus *bus, pci_route_irq_fn route_intx_to_irq)
+{
+    assert(!bus->parent_dev);
+    bus->route_intx_to_irq = route_intx_to_irq;
+}
+
+PCIINTxRoute pci_device_route_intx_to_irq(PCIDevice *dev, int pin)
+{
+    PCIBus *bus;
+
+    do {
+         bus = dev->bus;
+         pin = bus->map_irq(dev, pin);
+         dev = bus->parent_dev;
+    } while (dev);
+    assert(bus->route_intx_to_irq);
+    return bus->route_intx_to_irq(bus->irq_opaque, pin);
+}
+
 /***********************************************************/
 /* monitor info on PCI */
 
diff --git a/hw/pci.h b/hw/pci.h
index 6983b2f57a..7f7f88c6b9 100644
--- a/hw/pci.h
+++ b/hw/pci.h
@@ -141,6 +141,15 @@ enum {
 #define PCI_DEVICE_GET_CLASS(obj) \
      OBJECT_GET_CLASS(PCIDeviceClass, (obj), TYPE_PCI_DEVICE)
 
+typedef struct PCIINTxRoute {
+    enum {
+        PCI_INTX_ENABLED,
+        PCI_INTX_INVERTED,
+        PCI_INTX_DISABLED,
+    } mode;
+    int irq;
+} PCIINTxRoute;
+
 typedef struct PCIDeviceClass {
     DeviceClass parent_class;
 
@@ -278,6 +287,7 @@ MemoryRegion *pci_address_space_io(PCIDevice *dev);
 
 typedef void (*pci_set_irq_fn)(void *opaque, int irq_num, int level);
 typedef int (*pci_map_irq_fn)(PCIDevice *pci_dev, int irq_num);
+typedef PCIINTxRoute (*pci_route_irq_fn)(void *opaque, int pin);
 
 typedef enum {
     PCI_HOTPLUG_DISABLED,
@@ -306,6 +316,8 @@ PCIBus *pci_register_bus(DeviceState *parent, const char *name,
                          MemoryRegion *address_space_mem,
                          MemoryRegion *address_space_io,
                          uint8_t devfn_min, int nirq);
+void pci_bus_set_route_irq_fn(PCIBus *, pci_route_irq_fn);
+PCIINTxRoute pci_device_route_intx_to_irq(PCIDevice *dev, int pin);
 void pci_device_reset(PCIDevice *dev);
 void pci_bus_reset(PCIBus *bus);
 
diff --git a/hw/pci_internals.h b/hw/pci_internals.h
index 96690b72d3..d704704833 100644
--- a/hw/pci_internals.h
+++ b/hw/pci_internals.h
@@ -19,6 +19,7 @@ struct PCIBus {
     uint8_t devfn_min;
     pci_set_irq_fn set_irq;
     pci_map_irq_fn map_irq;
+    pci_route_irq_fn route_intx_to_irq;
     pci_hotplug_fn hotplug;
     DeviceState *hotplug_qdev;
     void *irq_opaque;
diff --git a/hw/piix_pci.c b/hw/piix_pci.c
index 09e84f59b6..8ece07c182 100644
--- a/hw/piix_pci.c
+++ b/hw/piix_pci.c
@@ -89,6 +89,7 @@ struct PCII440FXState {
 #define I440FX_SMRAM    0x72
 
 static void piix3_set_irq(void *opaque, int pirq, int level);
+static PCIINTxRoute piix3_route_intx_pin_to_irq(void *opaque, int pci_intx);
 static void piix3_write_config_xen(PCIDevice *dev,
                                uint32_t address, uint32_t val, int len);
 
@@ -315,6 +316,7 @@ static PCIBus *i440fx_common_init(const char *device_name,
                 pci_create_simple_multifunction(b, -1, true, "PIIX3"));
         pci_bus_irqs(b, piix3_set_irq, pci_slot_get_pirq, piix3,
                 PIIX_NUM_PIRQS);
+        pci_bus_set_route_irq_fn(b, piix3_route_intx_pin_to_irq);
     }
     piix3->pic = pic;
     *isa_bus = DO_UPCAST(ISABus, qbus,
@@ -386,6 +388,22 @@ static void piix3_set_irq(void *opaque, int pirq, int level)
     piix3_set_irq_level(piix3, pirq, level);
 }
 
+static PCIINTxRoute piix3_route_intx_pin_to_irq(void *opaque, int pin)
+{
+    PIIX3State *piix3 = opaque;
+    int irq = piix3->dev.config[PIIX_PIRQC + pin];
+    PCIINTxRoute route;
+
+    if (irq < PIIX_NUM_PIC_IRQS) {
+        route.mode = PCI_INTX_ENABLED;
+        route.irq = irq;
+    } else {
+        route.mode = PCI_INTX_DISABLED;
+        route.irq = -1;
+    }
+    return route;
+}
+
 /* irq routing is changed. so rebuild bitmap */
 static void piix3_update_irq_levels(PIIX3State *piix3)
 {