Re: [PATCH v6 2/4] vhost-vdpa: introduce SUSPEND backend feature bit

[Jason Wang]

On Fri, Jun 24, 2022 at 12:08 AM Eugenio Pérez <eperezma@xxxxxxxxxx> wrote:
>
> Userland knows if it can suspend the device or not by checking this feature
> bit.
>
> It's only offered if the vdpa driver backend implements the suspend()
> operation callback, and to offer it or userland to ack it if the backend
> does not offer that callback is an error.
>
> Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> ---
>  drivers/vhost/vdpa.c             | 16 +++++++++++++++-
>  include/uapi/linux/vhost_types.h |  2 ++
>  2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 23dcbfdfa13b..3d636e192061 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -347,6 +347,14 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
>         return 0;
>  }
>
> +static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
> +{
> +       struct vdpa_device *vdpa = v->vdpa;
> +       const struct vdpa_config_ops *ops = vdpa->config;
> +
> +       return ops->suspend;
> +}
> +
>  static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
>  {
>         struct vdpa_device *vdpa = v->vdpa;
> @@ -577,7 +585,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>         if (cmd == VHOST_SET_BACKEND_FEATURES) {
>                 if (copy_from_user(&features, featurep, sizeof(features)))
>                         return -EFAULT;
> -               if (features & ~VHOST_VDPA_BACKEND_FEATURES)
> +               if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
> +                                BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
> +                       return -EOPNOTSUPP;
> +               if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> +                    !vhost_vdpa_can_suspend(v))

Do we need to advertise this to the management?

Thanks

>                         return -EOPNOTSUPP;
>                 vhost_set_backend_features(&v->vdev, features);
>                 return 0;
> @@ -628,6 +640,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>                 break;
>         case VHOST_GET_BACKEND_FEATURES:
>                 features = VHOST_VDPA_BACKEND_FEATURES;
> +               if (vhost_vdpa_can_suspend(v))
> +                       features |= BIT_ULL(VHOST_BACKEND_F_SUSPEND);
>                 if (copy_to_user(featurep, &features, sizeof(features)))
>                         r = -EFAULT;
>                 break;
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index 634cee485abb..1bdd6e363f4c 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -161,5 +161,7 @@ struct vhost_vdpa_iova_range {
>   * message
>   */
>  #define VHOST_BACKEND_F_IOTLB_ASID  0x3
> +/* Device can be suspended */
> +#define VHOST_BACKEND_F_SUSPEND  0x4
>
>  #endif
> --
> 2.31.1
>