[PATCH] KVM: Resize kvm_io_bus_range array dynamically

[Amos Kong <akong@redhat.com>]

kvm_io_bus devices are used for ioevent, pit, pic, ioapic,
coalesced_mmio.

Currently Qemu only emulates one PCI bus, it contains 32 slots,
one slot contains 8 functions, maximum of supported PCI devices:
 1 * 32 * 8 = 256. The maximum of coalesced mmio zone is 100,
each zone has an iobus devices.

This patch makes the kvm_io_bus_range array can be resized dynamically.

Signed-off-by: Amos Kong <akong@redhat.com>
CC: Alex Williamson <alex.williamson@redhat.com>
---
 include/linux/kvm_host.h |    3 +--
 virt/kvm/kvm_main.c      |   24 +++++++++++++++---------
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 355e445..0e6d9d2 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -69,8 +69,7 @@ struct kvm_io_range {
 
 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..a6b9445 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,
@@ -2491,10 +2488,12 @@ 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)
-		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)
+		memcpy(new_bus, bus, sizeof(struct kvm_io_bus) +
+		       (bus->dev_count * sizeof(struct kvm_io_range)));
 	if (!new_bus)
 		return -ENOMEM;
 	kvm_io_bus_insert_dev(new_bus, dev, addr, len);
@@ -2514,16 +2513,23 @@ int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 
 	bus = kvm->buses[bus_idx];
 
-	new_bus = kmemdup(bus, sizeof(*bus), GFP_KERNEL);
+	new_bus = kmemdup(bus, sizeof(*bus) + ((bus->dev_count - 1) *
+			  sizeof(struct kvm_io_range)), 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) {
+		if (i == bus->dev_count - 1) {
+			/* dev is the last item of bus->range array,
+			   and new_bus->range doesn't have this item. */
+			r = 0;
+			new_bus->dev_count--;
+			break;
+		} else if (new_bus->range[i].dev == dev) {
 			r = 0;
 			new_bus->dev_count--;
-			new_bus->range[i] = new_bus->range[new_bus->dev_count];
+			new_bus->range[i] = 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);