Re: [PATCH v4] KVM: Resize kvm_io_range array dynamically

[Avi Kivity <avi@redhat.com>]

On 03/01/2012 09:01 AM, Amos Kong wrote:
> 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. One virtio-blk takes one iobus device,
> one virtio-net(vhost=on) takes two iobus devices.
> The maximum of coalesced mmio zone is 100, each zone
> has an iobus devices. So 300 io_bus devices are not enough.
>
> This patch makes the kvm_io_range array can be resized dynamically.
> Set an upper bounds for kvm_io_range to limit userspace.
> 1000 is a very large limit and not bloat the typical user.
>

Please separate the change to 1000 devs to a new patch.

>  
> +#define NR_IOBUS_DEVS 1000
> +
>  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..1baed68 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 +2488,14 @@ 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)
> +		memcpy(new_bus, bus, sizeof(*bus) + (bus->dev_count *
> +		       sizeof(struct kvm_io_range)));

This will be cleaner if you move the memcmp() after the check just below.

>  	if (!new_bus)
>  		return -ENOMEM;
>  	kvm_io_bus_insert_dev(new_bus, dev, addr, len);
> @@ -2513,26 +2514,28 @@ 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) {

The check is unneeded - if they compare equal, the copy is a no-op.

> +		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);
>

-- 
error compiling committee.c: too many arguments to function