KVM: make io_bus interface more robust

Today kvm_io_bus_regsiter_dev() returns void and will internally BUG_ON
if it fails.  We want to create dynamic MMIO/PIO entries driven from
userspace later in the series, so we need to enhance the code to be more
robust with the following changes:

   1) Add a return value to the registration function
   2) Fix up all the callsites to check the return code, handle any
      failures, and percolate the error up to the caller.
   3) Add an unregister function that collapses holes in the array

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

3 files changed, 46 insertions, 9 deletions

diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
index 0352f81..04d69cd 100644
--- a/virt/kvm/coalesced_mmio.c
+++ b/virt/kvm/coalesced_mmio.c
@@ -92,6 +92,7 @@ static const struct kvm_io_device_ops coalesced_mmio_ops = {
 int kvm_coalesced_mmio_init(struct kvm *kvm)
 {
 	struct kvm_coalesced_mmio_dev *dev;
+	int ret;
 
 	dev = kzalloc(sizeof(struct kvm_coalesced_mmio_dev), GFP_KERNEL);
 	if (!dev)
@@ -100,9 +101,12 @@ int kvm_coalesced_mmio_init(struct kvm *kvm)
 	kvm_iodevice_init(&dev->dev, &coalesced_mmio_ops);
 	dev->kvm = kvm;
 	kvm->coalesced_mmio_dev = dev;
-	kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &dev->dev);
 
-	return 0;
+	ret = kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &dev->dev);
+	if (ret < 0)
+		kfree(dev);
+
+	return ret;
 }
 
 int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index b91fbb2..fa05f67 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -342,6 +342,7 @@ static const struct kvm_io_device_ops ioapic_mmio_ops = {
 int kvm_ioapic_init(struct kvm *kvm)
 {
 	struct kvm_ioapic *ioapic;
+	int ret;
 
 	ioapic = kzalloc(sizeof(struct kvm_ioapic), GFP_KERNEL);
 	if (!ioapic)
@@ -350,7 +351,10 @@ int kvm_ioapic_init(struct kvm *kvm)
 	kvm_ioapic_reset(ioapic);
 	kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
 	ioapic->kvm = kvm;
-	kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &ioapic->dev);
-	return 0;
+	ret = kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &ioapic->dev);
+	if (ret < 0)
+		kfree(ioapic);
+
+	return ret;
 }
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fc1b58a..9c2fd02 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2533,21 +2533,50 @@ int kvm_io_bus_read(struct kvm_io_bus *bus, gpa_t addr, int len, void *val)
 	return -EOPNOTSUPP;
 }
 
-void kvm_io_bus_register_dev(struct kvm *kvm, struct kvm_io_bus *bus,
+int kvm_io_bus_register_dev(struct kvm *kvm, struct kvm_io_bus *bus,
 			     struct kvm_io_device *dev)
 {
+	int ret;
+
 	down_write(&kvm->slots_lock);
-	__kvm_io_bus_register_dev(bus, dev);
+	ret = __kvm_io_bus_register_dev(bus, dev);
 	up_write(&kvm->slots_lock);
+
+	return ret;
 }
 
 /* An unlocked version. Caller must have write lock on slots_lock. */
-void __kvm_io_bus_register_dev(struct kvm_io_bus *bus,
-			     struct kvm_io_device *dev)
+int __kvm_io_bus_register_dev(struct kvm_io_bus *bus,
+			      struct kvm_io_device *dev)
 {
-	BUG_ON(bus->dev_count > (NR_IOBUS_DEVS-1));
+	if (bus->dev_count > NR_IOBUS_DEVS-1)
+		return -ENOSPC;
 
 	bus->devs[bus->dev_count++] = dev;
+
+	return 0;
+}
+
+void kvm_io_bus_unregister_dev(struct kvm *kvm,
+			       struct kvm_io_bus *bus,
+			       struct kvm_io_device *dev)
+{
+	down_write(&kvm->slots_lock);
+	__kvm_io_bus_unregister_dev(bus, dev);
+	up_write(&kvm->slots_lock);
+}
+
+/* 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;
+
+	for (i = 0; i < bus->dev_count; i++)
+		if (bus->devs[i] == dev) {
+			bus->devs[i] = bus->devs[--bus->dev_count];
+			break;
+		}
 }
 
 static struct notifier_block kvm_cpu_notifier = {