Re: [Qemu-devel] [PATCH] kvm: exclude ioeventfd from counting kvm_io_range limit

[Gleb Natapov <gleb@redhat.com>]

On Sat, May 25, 2013 at 06:44:15AM +0800, Amos Kong wrote:
> We can easily reach the 1000 limit by start VM with a couple
> hundred I/O devices (multifunction=on). The hardcode limit
> already been adjusted 3 times (6 ~ 200 ~ 300 ~ 1000).
> 
> In userspace, we already have maximum file descriptor to
> limit ioeventfd count. But kvm_io_bus devices also are used
> for pit, pic, ioapic, coalesced_mmio. They couldn't be limited
> by maximum file descriptor.
> 
> Currently only ioeventfds take too much kvm_io_bus devices,
> so just exclude it from counting kvm_io_range limit.
> 
> Also fixed one indent issue in kvm_host.h
> 
> Signed-off-by: Amos Kong <akong@redhat.com>
Applied, thanks.

> ---
>  include/linux/kvm_host.h | 3 ++-
>  virt/kvm/eventfd.c       | 2 ++
>  virt/kvm/kvm_main.c      | 3 ++-
>  3 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f0eea07..ef261ab 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -144,7 +144,8 @@ struct kvm_io_range {
>  #define NR_IOBUS_DEVS 1000
>  
>  struct kvm_io_bus {
> -	int                   dev_count;
> +	int dev_count;
> +	int ioeventfd_count;
>  	struct kvm_io_range range[];
>  };
>  
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 64ee720..1550637 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -753,6 +753,7 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
>  	if (ret < 0)
>  		goto unlock_fail;
>  
> +	kvm->buses[bus_idx]->ioeventfd_count++;
>  	list_add_tail(&p->list, &kvm->ioeventfds);
>  
>  	mutex_unlock(&kvm->slots_lock);
> @@ -798,6 +799,7 @@ kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
>  			continue;
>  
>  		kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev);
> +		kvm->buses[bus_idx]->ioeventfd_count--;
>  		ioeventfd_release(p);
>  		ret = 0;
>  		break;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 302681c..c6d9baf 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2926,7 +2926,8 @@ 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)
> +	/* exclude ioeventfd which is limited by maximum fd */
> +	if (bus->dev_count - bus->ioeventfd_count > NR_IOBUS_DEVS - 1)
>  		return -ENOSPC;
>  
>  	new_bus = kzalloc(sizeof(*bus) + ((bus->dev_count + 1) *
> -- 
> 1.8.1.4

--
			Gleb.