[KVM PATCH v3 3/4] kvm: add io_bus unregister function

[Gregory Haskins]

We want to support the notion of dynamic MMIO/PIO registrations and
therefore will need to support both register as well as unregister.

However, the current io_bus code is structured as a linear array and
is not conducive to unregistering, so refactor to allow "holes" in the
array.  We then enhance the API with an unregister function.

Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx>
---

 include/linux/kvm_host.h |    4 +++-
 virt/kvm/kvm_main.c      |   48 ++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5289552..7dcae4b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -52,7 +52,7 @@ extern struct kmem_cache *kvm_vcpu_cache;
  * in one place.
  */
 struct kvm_io_bus {
-	int                   dev_count;
+	spinlock_t lock;
 #define NR_IOBUS_DEVS 6
 	struct kvm_io_device *devs[NR_IOBUS_DEVS];
 };
@@ -63,6 +63,8 @@ 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);
+int kvm_io_bus_unregister_dev(struct kvm_io_bus *bus,
+			    struct kvm_io_device *dev);
 
 struct kvm_vcpu {
 	struct kvm *kvm;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c71f276..4c36ac8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2435,16 +2435,18 @@ static struct notifier_block kvm_reboot_notifier = {
 void kvm_io_bus_init(struct kvm_io_bus *bus)
 {
 	memset(bus, 0, sizeof(*bus));
+	spin_lock_init(&bus->lock);
 }
 
 void kvm_io_bus_destroy(struct kvm_io_bus *bus)
 {
 	int i;
 
-	for (i = 0; i < bus->dev_count; i++) {
+	for (i = 0; i < NR_IOBUS_DEVS; i++) {
 		struct kvm_io_device *pos = bus->devs[i];
 
-		kvm_iodevice_destructor(pos);
+		if (pos)
+			kvm_iodevice_destructor(pos);
 	}
 }
 
@@ -2453,10 +2455,10 @@ struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
 {
 	int i;
 
-	for (i = 0; i < bus->dev_count; i++) {
+	for (i = 0; i < NR_IOBUS_DEVS; i++) {
 		struct kvm_io_device *pos = bus->devs[i];
 
-		if (pos->in_range(pos, addr, len, is_write))
+		if (pos && pos->in_range(pos, addr, len, is_write))
 			return pos;
 	}
 
@@ -2465,12 +2467,42 @@ struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
 
 int kvm_io_bus_register_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev)
 {
-	if (bus->dev_count > (NR_IOBUS_DEVS-1))
-		return -ENOSPC;
+	int i;
 
-	bus->devs[bus->dev_count++] = dev;
+	spin_lock(&bus->lock);
 
-	return 0;
+	for (i = 0; i < NR_IOBUS_DEVS; i++) {
+		if (bus->devs[i])
+			continue;
+
+		bus->devs[i] = dev;
+		spin_unlock(&bus->lock);
+		return 0;
+	}
+
+	spin_unlock(&bus->lock);
+
+	return -ENOSPC;
+}
+
+int kvm_io_bus_unregister_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev)
+{
+	int i;
+
+	spin_lock(&bus->lock);
+
+	for (i = 0; i < NR_IOBUS_DEVS; i++) {
+
+		if (bus->devs[i] == dev) {
+			bus->devs[i] = NULL;
+			spin_unlock(&bus->lock);
+			return 0;
+		}
+	}
+
+	spin_unlock(&bus->lock);
+
+	return -ENOENT;
 }
 
 static struct notifier_block kvm_cpu_notifier = {

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