Re: [PATCH] vhost-vdpa: Expose ASID group change after DRIVER_OK via backend feature

[Eugenio Perez Martin]

On Mon, May 11, 2026 at 11:46 AM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote:
>
> The commit in the fixes tag blocked VHOST_VDPA_SET_GROUP_ASID operations
> once DRIVER_OK is set. That is too strict for devices which can safely
> handle this during live migration flows.
>
> Bring back this behavior under a new vhost backend feature flag. The
> feature is supported by mlx5 and vdpa_sim devices.
>
> Fixes: 3543b04a4ea3 ("vhost: forbid change vq groups ASID if DRIVER_OK is set")
> Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
> Reviewed-by: Shahar Shitrit <shshitrit@xxxxxxxxxx>

Acked-by: Eugenio Pérez <eperezma@xxxxxxxxxx>

> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c |  3 ++-
>  drivers/vdpa/vdpa_sim/vdpa_sim.c  |  3 ++-
>  drivers/vhost/vdpa.c              | 13 +++++++++++--
>  include/uapi/linux/vhost_types.h  |  4 ++++
>  4 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index ad0d5fbbbca8..f89177957c76 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -2906,7 +2906,8 @@ static void unregister_link_notifier(struct mlx5_vdpa_net *ndev)
>
>  static u64 mlx5_vdpa_get_backend_features(const struct vdpa_device *vdpa)
>  {
> -       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK);
> +       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) |
> +              BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK);
>  }
>
>  static int mlx5_vdpa_set_driver_features(struct vdpa_device *vdev, u64 features)
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 8cb1cc2ea139..253c7fb35ea0 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -428,7 +428,8 @@ static u64 vdpasim_get_device_features(struct vdpa_device *vdpa)
>
>  static u64 vdpasim_get_backend_features(const struct vdpa_device *vdpa)
>  {
> -       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK);
> +       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) |
> +              BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK);
>  }
>
>  static int vdpasim_set_driver_features(struct vdpa_device *vdpa, u64 features)
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 692564b1bcbb..67b3f49fa709 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -682,7 +682,8 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>                         return -EFAULT;
>                 if (idx >= vdpa->ngroups || s.num >= vdpa->nas)
>                         return -EINVAL;
> -               if (ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK)
> +               if ((ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK) &&
> +                   !vhost_backend_has_feature(vq, VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK))
>                         return -EBUSY;
>                 if (!ops->set_group_asid)
>                         return -EOPNOTSUPP;
> @@ -791,7 +792,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>                                  BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST) |
>                                  BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
>                                  BIT_ULL(VHOST_BACKEND_F_RESUME) |
> -                                BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK)))
> +                                BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) |
> +                                BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK)))
>                         return -EOPNOTSUPP;
>                 if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
>                      !vhost_vdpa_can_suspend(v))
> @@ -805,6 +807,13 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>                 if ((features & BIT_ULL(VHOST_BACKEND_F_DESC_ASID)) &&
>                      !vhost_vdpa_has_desc_group(v))
>                         return -EOPNOTSUPP;

Ouch to me here. By reading the errno manual:

Nit: By reading errno(3):
ENOTSUP - Operation not supported (POSIX.1-2001).
EOPNOTSUPP - Operation not supported on socket (POSIX.1-2001).

I picked the wrong constant even if they share the same errno value
(by the same page of the manual). MST, is it worth changing it?

> +               if (features & BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK)) {
> +                       if (!(features & BIT_ULL(VHOST_BACKEND_F_IOTLB_ASID)))
> +                               return -EINVAL;
> +                       if (!(vhost_vdpa_get_backend_features(v) &
> +                               BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK)))
> +                               return -EOPNOTSUPP;
> +               }
>                 if ((features & BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST)) &&
>                      !vhost_vdpa_has_persistent_map(v))
>                         return -EOPNOTSUPP;
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index 1c39cc5f5a31..ec1ff8a2e260 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -197,5 +197,9 @@ struct vhost_vdpa_iova_range {
>  #define VHOST_BACKEND_F_DESC_ASID    0x7
>  /* IOTLB don't flush memory mapping across device reset */
>  #define VHOST_BACKEND_F_IOTLB_PERSIST  0x8
> +/* Device supports changing the group ASID after DRIVER_OK.
> + * Requires VHOST_BACKEND_F_IOTLB_ASID.
> + */
> +#define VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK  0x9
>
>  #endif
> --
> 2.54.0
>