diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 7fbedfd..0fcf660 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -74,6 +74,14 @@ config KVM_TRACE
 	  relayfs.  Note the ABI is not considered stable and will be
 	  modified in future updates.
 
+config KVM_MAX_IO_DEVICES
+	int "Maximum IO devices support per VM"
+	depends on KVM
+	default "256"
+	---help---
+	  This option influences the maximum number of MMIO, PIO, and other
+	  io-devices that can simultaneously register on a per-guest basis.
+
 # OK, it's a little counter-intuitive to do this, but it puts it neatly under
 # the virtualization menu.
 source drivers/lguest/Kconfig
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 1c41715..f24a8ea 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -621,13 +621,13 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
 
 	kvm_iodevice_init(&pit->dev, &pit_dev_ops);
-	ret = kvm_io_bus_register_dev(&kvm->pio_bus, &pit->dev);
+	ret = kvm_io_bus_register_dev(kvm, &kvm->pio_bus, &pit->dev);
 	if (ret < 0)
 		goto fail;
 
 	if (flags & KVM_PIT_SPEAKER_DUMMY) {
 		kvm_iodevice_init(&pit->speaker_dev, &speaker_dev_ops);
-		ret = kvm_io_bus_register_dev(&kvm->pio_bus,
+		ret = kvm_io_bus_register_dev(kvm, &kvm->pio_bus,
 					      &pit->speaker_dev);
 		if (ret < 0)
 			goto fail;
@@ -637,9 +637,10 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 
 fail:
 	if (flags & KVM_PIT_SPEAKER_DUMMY)
-		kvm_io_bus_unregister_dev(&kvm->pio_bus, &pit->speaker_dev);
+		kvm_io_bus_unregister_dev(kvm, &kvm->pio_bus,
+					  &pit->speaker_dev);
 
-	kvm_io_bus_unregister_dev(&kvm->pio_bus, &pit->dev);
+	kvm_io_bus_unregister_dev(kvm, &kvm->pio_bus, &pit->dev);
 
 	if (pit->irq_source_id >= 0)
 		kvm_free_irq_source_id(kvm, pit->irq_source_id);
diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
index 66e37c2..cfe3433 100644
--- a/arch/x86/kvm/i8259.c
+++ b/arch/x86/kvm/i8259.c
@@ -550,7 +550,7 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm)
 	 * Initialize PIO device
 	 */
 	kvm_iodevice_init(&s->dev, &picdev_ops);
-	ret = kvm_io_bus_register_dev(&kvm->pio_bus, &s->dev);
+	ret = kvm_io_bus_register_dev(kvm, &kvm->pio_bus, &s->dev);
 	if (ret < 0) {
 		kfree(s);
 		return NULL;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index eafa2b3..707c4d8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -61,10 +61,12 @@ void kvm_io_bus_init(struct kvm_io_bus *bus);
 void kvm_io_bus_destroy(struct kvm_io_bus *bus);
 struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
 					  gpa_t addr, int len, int is_write);
-int kvm_io_bus_register_dev(struct kvm_io_bus *bus,
-			    struct kvm_io_device *dev);
-void kvm_io_bus_unregister_dev(struct kvm_io_bus *bus,
+int kvm_io_bus_register_dev(struct kvm *kvm,
+			    struct kvm_io_bus *bus,
 			    struct kvm_io_device *dev);
+void kvm_io_bus_unregister_dev(struct kvm *kvm,
+			       struct kvm_io_bus *bus,
+			       struct kvm_io_device *dev);
 
 struct kvm_vcpu {
 	struct kvm *kvm;
@@ -139,6 +141,7 @@ struct kvm {
 	atomic_t online_vcpus;
 	struct list_head vm_list;
 	struct mutex lock;
+	unsigned long io_device_count;
 	struct kvm_io_bus mmio_bus;
 	struct kvm_io_bus pio_bus;
 #ifdef CONFIG_HAVE_KVM_EVENTFD
diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
index 3e89db8..09aae26 100644
--- a/virt/kvm/coalesced_mmio.c
+++ b/virt/kvm/coalesced_mmio.c
@@ -104,7 +104,7 @@ int kvm_coalesced_mmio_init(struct kvm *kvm)
 	dev->kvm = kvm;
 	kvm->coalesced_mmio_dev = dev;
 
-	ret = kvm_io_bus_register_dev(&kvm->mmio_bus, &dev->dev);
+	ret = kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &dev->dev);
 	if (ret < 0)
 		kfree(dev);
 
diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 28adb05..bc7ad68 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -345,7 +345,7 @@ int kvm_ioapic_init(struct kvm *kvm)
 	kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
 	ioapic->kvm = kvm;
 
-	ret = kvm_io_bus_register_dev(&kvm->mmio_bus, &ioapic->dev);
+	ret = kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &ioapic->dev);
 	if (ret < 0)
 		kfree(ioapic);
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6bd71f7..42cbea7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2482,18 +2482,25 @@ struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
 }
 
 /* assumes kvm->lock held */
-int kvm_io_bus_register_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev)
+int kvm_io_bus_register_dev(struct kvm *kvm,
+			    struct kvm_io_bus *bus,
+			    struct kvm_io_device *dev)
 {
 	if (bus->dev_count > (NR_IOBUS_DEVS-1))
 		return -ENOSPC;
 
+	if (kvm->io_device_count >= CONFIG_KVM_MAX_IO_DEVICES)
+		return -ENOSPC;
+
 	bus->devs[bus->dev_count++] = dev;
+	kvm->io_device_count++;
 
 	return 0;
 }
 
 /* assumes kvm->lock held */
-void kvm_io_bus_unregister_dev(struct kvm_io_bus *bus,
+void kvm_io_bus_unregister_dev(struct kvm *kvm,
+			       struct kvm_io_bus *bus,
 			       struct kvm_io_device *dev)
 {
 	int i;
@@ -2502,6 +2509,7 @@ void kvm_io_bus_unregister_dev(struct kvm_io_bus *bus,
 
 		if (bus->devs[i] == dev) {
 			bus->devs[i] = bus->devs[--bus->dev_count];
+			kvm->io_device_count--;
 			return;
 		}
 	}
