[PATCH v5 1/2] KVM: resize kvm_io_range array dynamically

[Amos Kong <akong@xxxxxxxxxx>]

This patch makes the kvm_io_range array can be resized dynamically.

Signed-off-by: Amos Kong <akong@xxxxxxxxxx>
---
 include/linux/kvm_host.h |    5 +++--
 virt/kvm/kvm_main.c      |   40 +++++++++++++++++++++-------------------
 2 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 355e445..e20dc8d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -67,10 +67,11 @@ struct kvm_io_range {
 	struct kvm_io_device *dev;
 };
 
+#define NR_IOBUS_DEVS 300
+
 struct kvm_io_bus {
 	int                   dev_count;
-#define NR_IOBUS_DEVS 300
-	struct kvm_io_range range[NR_IOBUS_DEVS];
+	struct kvm_io_range range[];
 };
 
 enum kvm_bus {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e4431ad..a0261d9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2389,9 +2389,6 @@ int kvm_io_bus_sort_cmp(const void *p1, const void *p2)
 int kvm_io_bus_insert_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev,
 			  gpa_t addr, int len)
 {
-	if (bus->dev_count == NR_IOBUS_DEVS)
-		return -ENOSPC;
-
 	bus->range[bus->dev_count++] = (struct kvm_io_range) {
 		.addr = addr,
 		.len = len,
@@ -2491,12 +2488,15 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 	struct kvm_io_bus *new_bus, *bus;
 
 	bus = kvm->buses[bus_idx];
-	if (bus->dev_count > NR_IOBUS_DEVS-1)
+	if (bus->dev_count > NR_IOBUS_DEVS - 1)
 		return -ENOSPC;
 
-	new_bus = kmemdup(bus, sizeof(struct kvm_io_bus), GFP_KERNEL);
+	new_bus = kzalloc(sizeof(*bus) + ((bus->dev_count + 1) *
+			  sizeof(struct kvm_io_range)), GFP_KERNEL);
 	if (!new_bus)
 		return -ENOMEM;
+	memcpy(new_bus, bus, sizeof(*bus) + (bus->dev_count *
+	       sizeof(struct kvm_io_range)));
 	kvm_io_bus_insert_dev(new_bus, dev, addr, len);
 	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
 	synchronize_srcu_expedited(&kvm->srcu);
@@ -2513,26 +2513,28 @@ int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 	struct kvm_io_bus *new_bus, *bus;
 
 	bus = kvm->buses[bus_idx];
-
-	new_bus = kmemdup(bus, sizeof(*bus), GFP_KERNEL);
-	if (!new_bus)
-		return -ENOMEM;
-
 	r = -ENOENT;
-	for (i = 0; i < new_bus->dev_count; i++)
-		if (new_bus->range[i].dev == dev) {
+	for (i = 0; i < bus->dev_count; i++)
+		if (bus->range[i].dev == dev) {
 			r = 0;
-			new_bus->dev_count--;
-			new_bus->range[i] = new_bus->range[new_bus->dev_count];
-			sort(new_bus->range, new_bus->dev_count,
-			     sizeof(struct kvm_io_range),
-			     kvm_io_bus_sort_cmp, NULL);
 			break;
 		}
 
-	if (r) {
-		kfree(new_bus);
+	if (r)
 		return r;
+
+	new_bus = kmemdup(bus, sizeof(*bus) + ((bus->dev_count - 1) *
+			  sizeof(struct kvm_io_range)), GFP_KERNEL);
+	if (!new_bus)
+		return -ENOMEM;
+
+	new_bus->dev_count--;
+	/* copy last entry of bus->range to deleted entry spot if
+	   deleted entry isn't the last entry of bus->range */
+	if (i != bus->dev_count - 1) {
+		new_bus->range[i] = bus->range[bus->dev_count - 1];
+		sort(new_bus->range, new_bus->dev_count,
+		     sizeof(struct kvm_io_range), kvm_io_bus_sort_cmp, NULL);
 	}
 
 	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);

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