diff --git a/Makefile b/Makefile
index e4a4002..8ca887f 100644
--- a/Makefile
+++ b/Makefile
@@ -138,7 +138,6 @@ ifeq ($(ARCH), powerpc)
 	DEFINES += -DCONFIG_PPC
 	OBJS	+= powerpc/boot.o
 	OBJS	+= powerpc/ioport.o
-	OBJS	+= powerpc/irq.o
 	OBJS	+= powerpc/kvm.o
 	OBJS	+= powerpc/cpu_info.o
 	OBJS	+= powerpc/kvm-cpu.o
@@ -153,7 +152,7 @@ ifeq ($(ARCH), powerpc)
 endif
 
 # ARM
-OBJS_ARM_COMMON		:= arm/fdt.o arm/gic.o arm/ioport.o arm/irq.o \
+OBJS_ARM_COMMON		:= arm/fdt.o arm/gic.o arm/ioport.o \
 			   arm/kvm.o arm/kvm-cpu.o arm/pci.o arm/timer.o \
 			   arm/pmu.o
 HDRS_ARM_COMMON		:= arm/include
@@ -186,7 +185,6 @@ ifeq ($(ARCH),mips)
 	ARCH_INCLUDE	:= mips/include
 	OBJS		+= mips/kvm.o
 	OBJS		+= mips/kvm-cpu.o
-	OBJS		+= mips/irq.o
 endif
 ###
 
diff --git a/arm/irq.c b/arm/irq.c
deleted file mode 100644
index d8f44df..0000000
--- a/arm/irq.c
+++ /dev/null
@@ -1,9 +0,0 @@
-#include "kvm/irq.h"
-#include "kvm/kvm.h"
-#include "kvm/util.h"
-
-int irq__add_msix_route(struct kvm *kvm, struct msi_msg *msg)
-{
-	die(__FUNCTION__);
-	return 0;
-}
diff --git a/hw/pci-shmem.c b/hw/pci-shmem.c
index a1c5ab7..7ce98cb 100644
--- a/hw/pci-shmem.c
+++ b/hw/pci-shmem.c
@@ -136,6 +136,8 @@ int pci_shmem__get_local_irqfd(struct kvm *kvm)
 
 		if (pci_shmem_pci_device.msix.ctrl & cpu_to_le16(PCI_MSIX_FLAGS_ENABLE)) {
 			gsi = irq__add_msix_route(kvm, &msix_table[0].msg);
+			if (gsi < 0)
+				return gsi;
 		} else {
 			gsi = pci_shmem_pci_device.irq_line;
 		}
diff --git a/include/kvm/irq.h b/include/kvm/irq.h
index 8a78e43..bb71521 100644
--- a/include/kvm/irq.h
+++ b/include/kvm/irq.h
@@ -10,11 +10,16 @@
 
 struct kvm;
 
+extern struct kvm_irq_routing *irq_routing;
+extern int next_gsi;
+
 int irq__alloc_line(void);
 int irq__get_nr_allocated_lines(void);
 
 int irq__init(struct kvm *kvm);
 int irq__exit(struct kvm *kvm);
+
+int irq__allocate_routing_entry(void);
 int irq__add_msix_route(struct kvm *kvm, struct msi_msg *msg);
 
 #endif
diff --git a/irq.c b/irq.c
index 71eaa05..c4b481c 100644
--- a/irq.c
+++ b/irq.c
@@ -1,7 +1,19 @@
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <linux/types.h>
+#include <linux/kvm.h>
+#include <errno.h>
+
+#include "kvm/kvm.h"
 #include "kvm/irq.h"
 #include "kvm/kvm-arch.h"
 
 static u8 next_line = KVM_IRQ_OFFSET;
+static int allocated_gsis = 0;
+
+int next_gsi;
+
+struct kvm_irq_routing *irq_routing = NULL;
 
 int irq__alloc_line(void)
 {
@@ -12,3 +24,74 @@ int irq__get_nr_allocated_lines(void)
 {
 	return next_line - KVM_IRQ_OFFSET;
 }
+
+int irq__allocate_routing_entry(void)
+{
+	size_t table_size = sizeof(struct kvm_irq_routing);
+	int nr_entries = 0;
+
+	if (irq_routing)
+		nr_entries = irq_routing->nr;
+
+	if (nr_entries < allocated_gsis)
+		return 0;
+
+	allocated_gsis = ALIGN(nr_entries + 1, 32);
+	table_size += sizeof(struct kvm_irq_routing_entry) * allocated_gsis;
+	irq_routing = realloc(irq_routing, table_size);
+
+	if (irq_routing == NULL)
+		return ENOMEM;
+
+	irq_routing->nr = nr_entries;
+
+	return 0;
+}
+
+static bool check_for_irq_routing(struct kvm *kvm)
+{
+	static int has_irq_routing = 0;
+
+	if (has_irq_routing == 0) {
+		if (kvm__supports_extension(kvm, KVM_CAP_IRQ_ROUTING))
+			has_irq_routing = 1;
+		else
+			has_irq_routing = -1;
+	}
+
+	return has_irq_routing > 0;
+}
+
+int irq__add_msix_route(struct kvm *kvm, struct msi_msg *msg)
+{
+	int r;
+
+	if (!check_for_irq_routing(kvm))
+		return -ENXIO;
+
+	r = irq__allocate_routing_entry();
+	if (r)
+		return r;
+
+	irq_routing->entries[irq_routing->nr++] =
+		(struct kvm_irq_routing_entry) {
+			.gsi = next_gsi,
+			.type = KVM_IRQ_ROUTING_MSI,
+			.u.msi.address_hi = msg->address_hi,
+			.u.msi.address_lo = msg->address_lo,
+			.u.msi.data = msg->data,
+		};
+
+	r = ioctl(kvm->vm_fd, KVM_SET_GSI_ROUTING, irq_routing);
+	if (r)
+		return r;
+
+	return next_gsi++;
+}
+
+int __attribute__((weak)) irq__exit(struct kvm *kvm)
+{
+	free(irq_routing);
+	return 0;
+}
+dev_base_exit(irq__exit);
diff --git a/mips/irq.c b/mips/irq.c
deleted file mode 100644
index c1ff6bb..0000000
--- a/mips/irq.c
+++ /dev/null
@@ -1,10 +0,0 @@
-#include "kvm/irq.h"
-#include "kvm/kvm.h"
-
-#include <stdlib.h>
-
-int irq__add_msix_route(struct kvm *kvm, struct msi_msg *msg)
-{
-	pr_warning("irq__add_msix_route");
-	return 1;
-}
diff --git a/powerpc/irq.c b/powerpc/irq.c
deleted file mode 100644
index 03f2fe7..0000000
--- a/powerpc/irq.c
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * PPC64 IRQ routines
- *
- * Copyright 2011 Matt Evans <matt@ozlabs.org>, IBM Corporation.
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published
- * by the Free Software Foundation.
- */
-
-#include "kvm/devices.h"
-#include "kvm/irq.h"
-#include "kvm/kvm.h"
-#include "kvm/util.h"
-
-#include <linux/types.h>
-#include <linux/rbtree.h>
-#include <linux/list.h>
-#include <linux/kvm.h>
-#include <sys/ioctl.h>
-
-#include <stddef.h>
-#include <stdlib.h>
-
-#include "kvm/pci.h"
-
-int irq__add_msix_route(struct kvm *kvm, struct msi_msg *msg)
-{
-	die(__FUNCTION__);
-	return 0;
-}
diff --git a/virtio/pci.c b/virtio/pci.c
index 90fcd64..072e5b7 100644
--- a/virtio/pci.c
+++ b/virtio/pci.c
@@ -156,7 +156,8 @@ static bool virtio_pci__specific_io_out(struct kvm *kvm, struct virtio_device *v
 					void *data, int size, int offset)
 {
 	struct virtio_pci *vpci = vdev->virtio;
-	u32 config_offset, gsi, vec;
+	u32 config_offset, vec;
+	int gsi;
 	int type = virtio__get_dev_specific_field(offset - 20, virtio_pci__msix_enabled(vpci),
 							&config_offset);
 	if (type == VIRTIO_PCI_O_MSIX) {
@@ -166,21 +167,27 @@ static bool virtio_pci__specific_io_out(struct kvm *kvm, struct virtio_device *v
 			if (vec == VIRTIO_MSI_NO_VECTOR)
 				break;
 
-			gsi = irq__add_msix_route(kvm, &vpci->msix_table[vec].msg);
-
-			vpci->config_gsi = gsi;
+			gsi = irq__add_msix_route(kvm,
+						  &vpci->msix_table[vec].msg);
+			if (gsi >= 0)
+				vpci->config_gsi = gsi;
 			break;
 		case VIRTIO_MSI_QUEUE_VECTOR:
-			vec = vpci->vq_vector[vpci->queue_selector] = ioport__read16(data);
+			vec = ioport__read16(data);
+			vpci->vq_vector[vpci->queue_selector] = vec;
 
 			if (vec == VIRTIO_MSI_NO_VECTOR)
 				break;
 
-			gsi = irq__add_msix_route(kvm, &vpci->msix_table[vec].msg);
+			gsi = irq__add_msix_route(kvm,
+						  &vpci->msix_table[vec].msg);
+			if (gsi < 0)
+				break;
 			vpci->gsis[vpci->queue_selector] = gsi;
 			if (vdev->ops->notify_vq_gsi)
 				vdev->ops->notify_vq_gsi(kvm, vpci->dev,
-							vpci->queue_selector, gsi);
+							 vpci->queue_selector,
+							 gsi);
 			break;
 		};
 
diff --git a/x86/irq.c b/x86/irq.c
index 72177e7..db465a1 100644
--- a/x86/irq.c
+++ b/x86/irq.c
@@ -11,20 +11,15 @@
 #include <stddef.h>
 #include <stdlib.h>
 
-#define IRQ_MAX_GSI			64
 #define IRQCHIP_MASTER			0
 #define IRQCHIP_SLAVE			1
 #define IRQCHIP_IOAPIC			2
 
-/* First 24 GSIs are routed between IRQCHIPs and IOAPICs */
-static u32 gsi = 24;
-
-struct kvm_irq_routing *irq_routing;
-
 static int irq__add_routing(u32 gsi, u32 type, u32 irqchip, u32 pin)
 {
-	if (gsi >= IRQ_MAX_GSI)
-		return -ENOSPC;
+	int r = irq__allocate_routing_entry();
+	if (r)
+		return r;
 
 	irq_routing->entries[irq_routing->nr++] =
 		(struct kvm_irq_routing_entry) {
@@ -41,11 +36,6 @@ int irq__init(struct kvm *kvm)
 {
 	int i, r;
 
-	irq_routing = calloc(sizeof(struct kvm_irq_routing) +
-			IRQ_MAX_GSI * sizeof(struct kvm_irq_routing_entry), 1);
-	if (irq_routing == NULL)
-		return -ENOMEM;
-
 	/* Hook first 8 GSIs to master IRQCHIP */
 	for (i = 0; i < 8; i++)
 		if (i != 2)
@@ -69,33 +59,8 @@ int irq__init(struct kvm *kvm)
 		return errno;
 	}
 
-	return 0;
-}
-dev_base_init(irq__init);
+	next_gsi = i;
 
-int irq__exit(struct kvm *kvm)
-{
-	free(irq_routing);
 	return 0;
 }
-dev_base_exit(irq__exit);
-
-int irq__add_msix_route(struct kvm *kvm, struct msi_msg *msg)
-{
-	int r;
-
-	irq_routing->entries[irq_routing->nr++] =
-		(struct kvm_irq_routing_entry) {
-			.gsi = gsi,
-			.type = KVM_IRQ_ROUTING_MSI,
-			.u.msi.address_hi = msg->address_hi,
-			.u.msi.address_lo = msg->address_lo,
-			.u.msi.data = msg->data,
-		};
-
-	r = ioctl(kvm->vm_fd, KVM_SET_GSI_ROUTING, irq_routing);
-	if (r)
-		return r;
-
-	return gsi++;
-}
+dev_base_init(irq__init);
