Linux Virtualization - Sep 2021 - [PATCH 5/6] vdpa: add get_vq_num_unchangeable callback in vdpa_config_ops

On Wed, Sep 8, 2021 at 8:23 PM Wu Zongyong <wuzongyong at
linux.alibaba.com> wrote:
>
> This new callback is used to indicate whether the vring size can be
> change or not. It is useful when we have a legacy virtio pci device as
> the vdpa device for there is no way to negotiate the vring num by the
> specification.
So I'm not sure it's worth bothering. E.g what if we just fail
VHOST_SET_VRING_NUM it the value doesn't match what hardware has?

Thanks
>
> Signed-off-by: Wu Zongyong <wuzongyong at linux.alibaba.com>
> ---
>  drivers/vhost/vdpa.c         | 19 +++++++++++++++++++
>  drivers/virtio/virtio_vdpa.c |  5 ++++-
>  include/linux/vdpa.h         |  4 ++++
>  include/uapi/linux/vhost.h   |  2 ++
>  4 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 9479f7f79217..2204d27d1e5d 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -350,6 +350,22 @@ static long vhost_vdpa_get_iova_range(struct
vhost_vdpa *v, u32 __user *argp)
>         return 0;
>  }
>
> +static long vhost_vdpa_get_vring_num_unchangeable(struct vhost_vdpa *v,
> +                                                 u32 __user *argp)
> +{
> +       struct vdpa_device *vdpa = v->vdpa;
> +       const struct vdpa_config_ops *ops = vdpa->config;
> +       bool unchangeable = false;
> +
> +       if (ops->get_vq_num_unchangeable)
> +               unchangeable = ops->get_vq_num_unchangeable(vdpa);
> +
> +       if (copy_to_user(argp, &unchangeable, sizeof(unchangeable)))
> +               return -EFAULT;
> +
> +       return 0;
> +}
> +
>  static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>                                    void __user *argp)
>  {
> @@ -487,6 +503,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file
*filep,
>         case VHOST_VDPA_GET_IOVA_RANGE:
>                 r = vhost_vdpa_get_iova_range(v, argp);
>                 break;
> +       case VHOST_VDPA_GET_VRING_NUM_UNCHANGEABLE:
> +               r = vhost_vdpa_get_vring_num_unchangeable(v, argp);
> +               break;
>         default:
>                 r = vhost_dev_ioctl(&v->vdev, cmd, argp);
>                 if (r == -ENOIOCTLCMD)
> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> index 72eaef2caeb1..afb47465307a 100644
> --- a/drivers/virtio/virtio_vdpa.c
> +++ b/drivers/virtio/virtio_vdpa.c
> @@ -146,6 +146,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev,
unsigned int index,
>         struct vdpa_vq_state state = {0};
>         unsigned long flags;
>         u32 align, num;
> +       bool may_reduce_num = true;
>         int err;
>
>         if (!name)
> @@ -171,8 +172,10 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev,
unsigned int index,
>
>         /* Create the vring */
>         align = ops->get_vq_align(vdpa);
> +       if (ops->get_vq_num_unchangeable)
> +               may_reduce_num = !ops->get_vq_num_unchangeable(vdpa);
>         vq = vring_create_virtqueue(index, num, align, vdev,
> -                                   true, true, ctx,
> +                                   true, may_reduce_num, ctx,
>                                     virtio_vdpa_notify, callback, name);
>         if (!vq) {
>                 err = -ENOMEM;
> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> index 35648c11e312..f809b7ada00d 100644
> --- a/include/linux/vdpa.h
> +++ b/include/linux/vdpa.h
> @@ -195,6 +195,9 @@ struct vdpa_iova_range {
>   *                             @vdev: vdpa device
>   *                             Returns the iova range supported by
>   *                             the device.
> + * @get_vq_num_unchangeable    Check if size of virtqueue is unchangeable
(optional)
> + *                             @vdev: vdpa device
> + *                             Returns boolean: unchangeable (true) or not
(false)
>   * @set_map:                   Set device memory mapping (optional)
>   *                             Needed for device that using device
>   *                             specific DMA translation (on-chip IOMMU)
> @@ -262,6 +265,7 @@ struct vdpa_config_ops {
>                            const void *buf, unsigned int len);
>         u32 (*get_generation)(struct vdpa_device *vdev);
>         struct vdpa_iova_range (*get_iova_range)(struct vdpa_device *vdev);
> +       bool (*get_vq_num_unchangeable)(struct vdpa_device *vdev);
>
>         /* DMA ops */
>         int (*set_map)(struct vdpa_device *vdev, struct vhost_iotlb
*iotlb);
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index c998860d7bbc..184f1f7f8498 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -150,4 +150,6 @@
>  /* Get the valid iova range */
>  #define VHOST_VDPA_GET_IOVA_RANGE      _IOR(VHOST_VIRTIO, 0x78, \
>                                              struct vhost_vdpa_iova_range)
> +/* Check if the vring size can be change */
> +#define VHOST_VDPA_GET_VRING_NUM_UNCHANGEABLE _IOR(VHOST_VIRTIO, 0X79,
bool)
>  #endif
> --
> 2.31.1
>

On Thu, Sep 09, 2021 at 10:55:03AM +0800, Jason Wang
wrote:
> On Wed, Sep 8, 2021 at 8:23 PM Wu Zongyong <wuzongyong at
linux.alibaba.com> wrote:
> >
> > This new callback is used to indicate whether the vring size can be
> > change or not. It is useful when we have a legacy virtio pci device as
> > the vdpa device for there is no way to negotiate the vring num by the
> > specification.
> 
> So I'm not sure it's worth bothering. E.g what if we just fail
> VHOST_SET_VRING_NUM it the value doesn't match what hardware has?
> 
> Thanks
More importantly is there and actual plan for supporting
legacy devices? I don't think they currently work at a number
of levels.

-- 
MST