Re: [PATCH 2/4] vhost-vdpa: Introduce RESUME backend feature bit

* Re: [PATCH 2/4] vhost-vdpa: Introduce RESUME backend feature bit
       [not found] ` <72bdc9ae91ca4ed8a2c9ea2aab53f8e04d4512f6.1665674878.git.sebastien.boeuf@intel.com>
@ 2022-10-14  5:58   ` Jason Wang
  2022-10-14  6:05     ` Michael S. Tsirkin
  0 siblings, 1 reply; 7+ messages in thread
From: Jason Wang @ 2022-10-14  5:58 UTC (permalink / raw)
  To: sebastien.boeuf; +Cc: eperezma, mst, virtualization

On Thu, Oct 13, 2022 at 11:35 PM <sebastien.boeuf@intel.com> wrote:
>
> From: Sebastien Boeuf <sebastien.boeuf@intel.com>
>
> Userspace knows if the device can be resumed or not by checking this
> feature bit.
>
> It's only exposed if the vdpa driver backend implements the resume()
> operation callback. Userspace trying to negotiate this feature when it
> hasn't been exposed will result in an error.
>
> Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
> ---
>  drivers/vhost/vdpa.c             | 19 ++++++++++++++++++-
>  include/uapi/linux/vhost_types.h |  2 ++
>  2 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 166044642fd5..161727e1a9a5 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -355,6 +355,14 @@ static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
>         return ops->suspend;
>  }
>
> +static bool vhost_vdpa_can_resume(const struct vhost_vdpa *v)
> +{
> +       struct vdpa_device *vdpa = v->vdpa;
> +       const struct vdpa_config_ops *ops = vdpa->config;
> +
> +       return ops->resume;
> +}
> +
>  static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
>  {
>         struct vdpa_device *vdpa = v->vdpa;
> @@ -602,11 +610,18 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>                 if (copy_from_user(&features, featurep, sizeof(features)))
>                         return -EFAULT;
>                 if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
> -                                BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
> +                                BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
> +                                BIT_ULL(VHOST_BACKEND_F_RESUME)))
>                         return -EOPNOTSUPP;
>                 if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
>                      !vhost_vdpa_can_suspend(v))
>                         return -EOPNOTSUPP;
> +               if ((features & BIT_ULL(VHOST_BACKEND_F_RESUME)) &&
> +                    !vhost_vdpa_can_resume(v))
> +                       return -EOPNOTSUPP;
> +               if (!(features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> +                    (features & BIT_ULL(VHOST_BACKEND_F_RESUME)))
> +                       return -EINVAL;

Is it better to do the check during the probe? It should be a bug that
we're having a parent that can only do resume but not suspend.

Thanks

>                 vhost_set_backend_features(&v->vdev, features);
>                 return 0;
>         }
> @@ -658,6 +673,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>                 features = VHOST_VDPA_BACKEND_FEATURES;
>                 if (vhost_vdpa_can_suspend(v))
>                         features |= BIT_ULL(VHOST_BACKEND_F_SUSPEND);
> +               if (vhost_vdpa_can_resume(v))
> +                       features |= BIT_ULL(VHOST_BACKEND_F_RESUME);
>                 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 53601ce2c20a..c5690a8992d8 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -163,5 +163,7 @@ struct vhost_vdpa_iova_range {
>  #define VHOST_BACKEND_F_IOTLB_ASID  0x3
>  /* Device can be suspended */
>  #define VHOST_BACKEND_F_SUSPEND  0x4
> +/* Device can be resumed */
> +#define VHOST_BACKEND_F_RESUME  0x5
>
>  #endif
> --
> 2.34.1
>
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