diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index b2e4d16..d0ad538 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -241,10 +241,10 @@ static int handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	return 0;
 mmio:
 	if (p->dir)
-		r = kvm_io_bus_read(&vcpu->kvm->mmio_bus, p->addr,
+		r = kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, p->addr,
 				    p->size, &p->data);
 	else
-		r = kvm_io_bus_write(&vcpu->kvm->mmio_bus, p->addr,
+		r = kvm_io_bus_write(vcpu->kvm, KVM_MMIO_BUS, p->addr,
 				     p->size, &p->data);
 	if (r)
 		printk(KERN_ERR"kvm: No iodevice found! addr:%lx\n", p->addr);
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 296aba4..a7259e8 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -642,13 +642,13 @@ 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_unregister;
@@ -657,7 +657,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	return pit;
 
 fail_unregister:
-	__kvm_io_bus_unregister_dev(&kvm->pio_bus, &pit->dev);
+	kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &pit->dev);
 
 fail:
 	if (pit->irq_source_id >= 0)
diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
index d057c0c..b7d145b 100644
--- a/arch/x86/kvm/i8259.c
+++ b/arch/x86/kvm/i8259.c
@@ -533,7 +533,9 @@ 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, &kvm->pio_bus, &s->dev);
+	down_write(&kvm->slots_lock);
+	ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, &s->dev);
+	up_write(&kvm->slots_lock);
 	if (ret < 0) {
 		kfree(s);
 		return NULL;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 59f4da4..b9adeae 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2852,7 +2852,7 @@ static int vcpu_mmio_write(struct kvm_vcpu *vcpu, gpa_t addr, int len,
 	    !kvm_iodevice_write(&vcpu->arch.apic->dev, addr, len, v))
 		return 0;
 
-	return kvm_io_bus_write(&vcpu->kvm->mmio_bus, addr, len, v);
+	return kvm_io_bus_write(vcpu->kvm, KVM_MMIO_BUS, addr, len, v);
 }
 
 static int vcpu_mmio_read(struct kvm_vcpu *vcpu, gpa_t addr, int len, void *v)
@@ -2861,7 +2861,7 @@ static int vcpu_mmio_read(struct kvm_vcpu *vcpu, gpa_t addr, int len, void *v)
 	    !kvm_iodevice_read(&vcpu->arch.apic->dev, addr, len, v))
 		return 0;
 
-	return kvm_io_bus_read(&vcpu->kvm->mmio_bus, addr, len, v);
+	return kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, addr, len, v);
 }
 
 static int kvm_read_guest_virt(gva_t addr, void *val, unsigned int bytes,
@@ -3346,11 +3346,12 @@ static int kernel_pio(struct kvm_vcpu *vcpu, void *pd)
 	int r;
 
 	if (vcpu->arch.pio.in)
-		r = kvm_io_bus_read(&vcpu->kvm->pio_bus, vcpu->arch.pio.port,
+		r = kvm_io_bus_read(vcpu->kvm, KVM_PIO_BUS, vcpu->arch.pio.port,
 				    vcpu->arch.pio.size, pd);
 	else
-		r = kvm_io_bus_write(&vcpu->kvm->pio_bus, vcpu->arch.pio.port,
-				     vcpu->arch.pio.size, pd);
+		r = kvm_io_bus_write(vcpu->kvm, KVM_PIO_BUS,
+				     vcpu->arch.pio.port, vcpu->arch.pio.size,
+				     pd);
 	return r;
 }
 
@@ -3361,7 +3362,7 @@ static int pio_string_write(struct kvm_vcpu *vcpu)
 	int i, r = 0;
 
 	for (i = 0; i < io->cur_count; i++) {
-		if (kvm_io_bus_write(&vcpu->kvm->pio_bus,
+		if (kvm_io_bus_write(vcpu->kvm, KVM_PIO_BUS,
 				     io->port, io->size, pd)) {
 			r = -EOPNOTSUPP;
 			break;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 20941c0..5e9cb90 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -57,20 +57,20 @@ struct kvm_io_bus {
 	struct kvm_io_device *devs[NR_IOBUS_DEVS];
 };
 
-void kvm_io_bus_init(struct kvm_io_bus *bus);
-void kvm_io_bus_destroy(struct kvm_io_bus *bus);
-int kvm_io_bus_write(struct kvm_io_bus *bus, gpa_t addr, int len,
-		     const void *val);
-int kvm_io_bus_read(struct kvm_io_bus *bus, gpa_t addr, int len,
+enum kvm_bus {
+	KVM_MMIO_BUS,
+	KVM_PIO_BUS,
+	KVM_NR_BUSES
+};
+
+int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
+		     int len, const void *val);
+int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int len,
 		    void *val);
-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,
+int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 			    struct kvm_io_device *dev);
-void __kvm_io_bus_unregister_dev(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);
+int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
+			      struct kvm_io_device *dev);
 
 struct kvm_vcpu {
 	struct kvm *kvm;
@@ -171,8 +171,7 @@ struct kvm {
 	atomic_t online_vcpus;
 	struct list_head vm_list;
 	struct mutex lock;
-	struct kvm_io_bus mmio_bus;
-	struct kvm_io_bus pio_bus;
+	struct kvm_io_bus *buses[KVM_NR_BUSES];
 #ifdef CONFIG_HAVE_KVM_EVENTFD
 	struct {
 		spinlock_t        lock;
diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
index d68e6c6..a736a93 100644
--- a/virt/kvm/coalesced_mmio.c
+++ b/virt/kvm/coalesced_mmio.c
@@ -110,7 +110,9 @@ int kvm_coalesced_mmio_init(struct kvm *kvm)
 	dev->kvm = kvm;
 	kvm->coalesced_mmio_dev = dev;
 
-	ret = kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &dev->dev);
+	down_write(&kvm->slots_lock);
+	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, &dev->dev);
+	up_write(&kvm->slots_lock);
 	if (ret < 0)
 		goto out_free_dev;
 
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index a9d3fc6..315a586 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -463,7 +463,7 @@ static int
 kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 {
 	int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
-	struct kvm_io_bus        *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus;
+	enum kvm_bus              bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
 	struct _ioeventfd        *p;
 	struct eventfd_ctx       *eventfd;
 	int                       ret;
@@ -518,7 +518,7 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 
 	kvm_iodevice_init(&p->dev, &ioeventfd_ops);
 
-	ret = __kvm_io_bus_register_dev(bus, &p->dev);
+	ret = kvm_io_bus_register_dev(kvm, bus_idx, &p->dev);
 	if (ret < 0)
 		goto unlock_fail;
 
@@ -542,7 +542,7 @@ static int
 kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 {
 	int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
-	struct kvm_io_bus        *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus;
+	enum kvm_bus              bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
 	struct _ioeventfd        *p, *tmp;
 	struct eventfd_ctx       *eventfd;
 	int                       ret = -ENOENT;
@@ -565,7 +565,7 @@ kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 		if (!p->wildcard && p->datamatch != args->datamatch)
 			continue;
 
-		__kvm_io_bus_unregister_dev(bus, &p->dev);
+		kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev);
 		ioeventfd_release(p);
 		ret = 0;
 		break;
diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 38a2d20..f326a6f 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -372,7 +372,9 @@ int kvm_ioapic_init(struct kvm *kvm)
 	kvm_ioapic_reset(ioapic);
 	kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
 	ioapic->kvm = kvm;
-	ret = kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &ioapic->dev);
+	down_write(&kvm->slots_lock);
+	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, &ioapic->dev);
+	up_write(&kvm->slots_lock);
 	if (ret < 0)
 		kfree(ioapic);
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c680f7b..659bc12 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -85,6 +85,8 @@ static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl,
 static int hardware_enable_all(void);
 static void hardware_disable_all(void);
 
+static void kvm_io_bus_destroy(struct kvm_io_bus *bus);
+
 static bool kvm_rebooting;
 
 static bool largepages_enabled = true;
@@ -367,7 +369,7 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
 
 static struct kvm *kvm_create_vm(void)
 {
-	int r = 0;
+	int r = 0, i;
 	struct kvm *kvm = kvm_arch_create_vm();
 #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
 	struct page *page;
@@ -391,6 +393,14 @@ static struct kvm *kvm_create_vm(void)
 		goto out_err;
 	if (init_srcu_struct(&kvm->srcu))
 		goto out_err;
+	for (i = 0; i < KVM_NR_BUSES; i++) {
+		kvm->buses[i] = kzalloc(sizeof(struct kvm_io_bus),
+					GFP_KERNEL);
+		if (!kvm->buses[i]) {
+			cleanup_srcu_struct(&kvm->srcu);
+			goto out_err;
+		}
+	}
 
 #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
 	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
@@ -416,11 +426,9 @@ static struct kvm *kvm_create_vm(void)
 	atomic_inc(&kvm->mm->mm_count);
 	spin_lock_init(&kvm->mmu_lock);
 	spin_lock_init(&kvm->requests_lock);
-	kvm_io_bus_init(&kvm->pio_bus);
 	kvm_eventfd_init(kvm);
 	mutex_init(&kvm->lock);
 	mutex_init(&kvm->irq_lock);
-	kvm_io_bus_init(&kvm->mmio_bus);
 	init_rwsem(&kvm->slots_lock);
 	atomic_set(&kvm->users_count, 1);
 	spin_lock(&kvm_lock);
@@ -435,6 +443,8 @@ out:
 out_err:
 	hardware_disable_all();
 out_err_nodisable:
+	for (i = 0; i < KVM_NR_BUSES; i++)
+		kfree(kvm->buses[i]);
 	kfree(kvm->memslots);
 	kfree(kvm);
 	return ERR_PTR(r);
@@ -480,6 +490,7 @@ void kvm_free_physmem(struct kvm *kvm)
 
 static void kvm_destroy_vm(struct kvm *kvm)
 {
+	int i;
 	struct mm_struct *mm = kvm->mm;
 
 	kvm_arch_sync_events(kvm);
@@ -487,8 +498,8 @@ static void kvm_destroy_vm(struct kvm *kvm)
 	list_del(&kvm->vm_list);
 	spin_unlock(&kvm_lock);
 	kvm_free_irq_routing(kvm);
-	kvm_io_bus_destroy(&kvm->pio_bus);
-	kvm_io_bus_destroy(&kvm->mmio_bus);
+	for (i = 0; i < KVM_NR_BUSES; i++)
+		kvm_io_bus_destroy(kvm->buses[i]);
 	kvm_coalesced_mmio_free(kvm);
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
 	mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm);
@@ -1949,12 +1960,7 @@ static struct notifier_block kvm_reboot_notifier = {
 	.priority = 0,
 };
 
-void kvm_io_bus_init(struct kvm_io_bus *bus)
-{
-	memset(bus, 0, sizeof(*bus));
-}
-
-void kvm_io_bus_destroy(struct kvm_io_bus *bus)
+static void kvm_io_bus_destroy(struct kvm_io_bus *bus)
 {
 	int i;
 
@@ -1963,13 +1969,15 @@ void kvm_io_bus_destroy(struct kvm_io_bus *bus)
 
 		kvm_iodevice_destructor(pos);
 	}
+	kfree(bus);
 }
 
 /* kvm_io_bus_write - called under kvm->slots_lock */
-int kvm_io_bus_write(struct kvm_io_bus *bus, gpa_t addr,
+int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 		     int len, const void *val)
 {
 	int i;
+	struct kvm_io_bus *bus = rcu_dereference(kvm->buses[bus_idx]);
 	for (i = 0; i < bus->dev_count; i++)
 		if (!kvm_iodevice_write(bus->devs[i], addr, len, val))
 			return 0;
@@ -1977,59 +1985,71 @@ int kvm_io_bus_write(struct kvm_io_bus *bus, gpa_t addr,
 }
 
 /* kvm_io_bus_read - called under kvm->slots_lock */
-int kvm_io_bus_read(struct kvm_io_bus *bus, gpa_t addr, int len, void *val)
+int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
+		    int len, void *val)
 {
 	int i;
+	struct kvm_io_bus *bus = rcu_dereference(kvm->buses[bus_idx]);
+
 	for (i = 0; i < bus->dev_count; i++)
 		if (!kvm_iodevice_read(bus->devs[i], addr, len, val))
 			return 0;
 	return -EOPNOTSUPP;
 }
 
-int kvm_io_bus_register_dev(struct kvm *kvm, struct kvm_io_bus *bus,
-			     struct kvm_io_device *dev)
+/* Caller must have write lock on slots_lock. */
+int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx,
+			    struct kvm_io_device *dev)
 {
-	int ret;
-
-	down_write(&kvm->slots_lock);
-	ret = __kvm_io_bus_register_dev(bus, dev);
-	up_write(&kvm->slots_lock);
+	struct kvm_io_bus *new_bus, *bus;
 
-	return ret;
-}
-
-/* An unlocked version. Caller must have write lock on slots_lock. */
-int __kvm_io_bus_register_dev(struct kvm_io_bus *bus,
-			      struct kvm_io_device *dev)
-{
+	bus = kvm->buses[bus_idx];
 	if (bus->dev_count > NR_IOBUS_DEVS-1)
 		return -ENOSPC;
 
-	bus->devs[bus->dev_count++] = dev;
+	new_bus = kzalloc(sizeof(struct kvm_io_bus), GFP_KERNEL);
+	if (!new_bus)
+		return -ENOMEM;
+	memcpy(new_bus, bus, sizeof(struct kvm_io_bus));
+	new_bus->devs[new_bus->dev_count++] = dev;
+	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
+	synchronize_srcu_expedited(&kvm->srcu);
+	kfree(bus);
 
 	return 0;
 }
 
-void kvm_io_bus_unregister_dev(struct kvm *kvm,
-			       struct kvm_io_bus *bus,
-			       struct kvm_io_device *dev)
+/* Caller must have write lock on slots_lock. */
+int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
+			      struct kvm_io_device *dev)
 {
-	down_write(&kvm->slots_lock);
-	__kvm_io_bus_unregister_dev(bus, dev);
-	up_write(&kvm->slots_lock);
-}
+	int i, r;
+	struct kvm_io_bus *new_bus, *bus;
 
-/* An unlocked version. Caller must have write lock on slots_lock. */
-void __kvm_io_bus_unregister_dev(struct kvm_io_bus *bus,
-				 struct kvm_io_device *dev)
-{
-	int i;
+	new_bus = kzalloc(sizeof(struct kvm_io_bus), GFP_KERNEL);
+	if (!new_bus)
+		return -ENOMEM;
 
-	for (i = 0; i < bus->dev_count; i++)
-		if (bus->devs[i] == dev) {
-			bus->devs[i] = bus->devs[--bus->dev_count];
+	bus = kvm->buses[bus_idx];
+	memcpy(new_bus, bus, sizeof(struct kvm_io_bus));
+
+	r = -ENOENT;
+	for (i = 0; i < new_bus->dev_count; i++)
+		if (new_bus->devs[i] == dev) {
+			r = 0;
+			new_bus->devs[i] = new_bus->devs[--new_bus->dev_count];
 			break;
 		}
+
+	if (r) {
+		kfree(new_bus);
+		return r;
+	}
+
+	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
+	synchronize_srcu_expedited(&kvm->srcu);
+	kfree(bus);
+	return r;
 }
 
 static struct notifier_block kvm_cpu_notifier = {
