Re: [Qemu-devel] [PATCH 3/8] virtio: Add support for guest setting of queue size

[Anthony Liguori <aliguori@us.ibm.com>]

Peter Maydell <peter.maydell@linaro.org> writes:

> The MMIO virtio transport spec allows the guest to tell the host how
> large the queue size is. Add virtio_queue_set_num() function which
> implements this in the QEMU common virtio support code.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/virtio/virtio.c         |    6 ++++++
>  include/hw/virtio/virtio.h |    1 +
>  2 files changed, 7 insertions(+)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 8176c14..8805b8a 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -667,6 +667,12 @@ hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n)
>      return vdev->vq[n].pa;
>  }
>  
> +void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
> +{
> +    vdev->vq[n].vring.num = num;
> +    virtqueue_init(&vdev->vq[n]);

I think some level of checking is probably needed on num since we do a
tremendous amount of math on it.  I doubt it's exploitable since it's
always treated as a PA, but better to be safe than sorry.

Regards,

Anthony Liguori

> +}
> +
>  int virtio_queue_get_num(VirtIODevice *vdev, int n)
>  {
>      return vdev->vq[n].vring.num;
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index a6c5c53..95c4772 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -198,6 +198,7 @@ void virtio_config_writew(VirtIODevice *vdev, uint32_t addr, uint32_t data);
>  void virtio_config_writel(VirtIODevice *vdev, uint32_t addr, uint32_t data);
>  void virtio_queue_set_addr(VirtIODevice *vdev, int n, hwaddr addr);
>  hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n);
> +void virtio_queue_set_num(VirtIODevice *vdev, int n, int num);
>  int virtio_queue_get_num(VirtIODevice *vdev, int n);
>  void virtio_queue_notify(VirtIODevice *vdev, int n);
>  uint16_t virtio_queue_vector(VirtIODevice *vdev, int n);
> -- 
> 1.7.9.5