Re: [RFC] vdpa/mlx5: preserve CVQ vringh index

[Eugenio Perez Martin]

On Thu, Oct 26, 2023 at 10:09 PM Steve Sistare
<steven.sistare@xxxxxxxxxx> wrote:
>
> mlx5_vdpa does not preserve userland's view of vring base for the control
> queue in the following sequence:
>
> ioctl VHOST_SET_VRING_BASE
> ioctl VHOST_VDPA_SET_STATUS VIRTIO_CONFIG_S_DRIVER_OK
>   mlx5_vdpa_set_status()
>     setup_cvq_vring()
>       vringh_init_iotlb()
>         vringh_init_kern()
>           vrh->last_avail_idx = 0;
> ioctl VHOST_GET_VRING_BASE
>
> To fix, restore the value of cvq->vring.last_avail_idx after calling
> vringh_init_iotlb.
>
> Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c |  7 ++++++-
>  drivers/vhost/vringh.c            | 30 ++++++++++++++++++++++++++++++
>  include/linux/vringh.h            |  2 ++
>  3 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 946488b8989f..f64758143115 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -2795,13 +2795,18 @@ static int setup_cvq_vring(struct mlx5_vdpa_dev *mvdev)
>         struct mlx5_control_vq *cvq = &mvdev->cvq;
>         int err = 0;
>
> -       if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ))
> +       if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)) {
> +               u16 last_avail_idx = cvq->vring.last_avail_idx;
> +
>                 err = vringh_init_iotlb(&cvq->vring, mvdev->actual_features,
>                                         MLX5_CVQ_MAX_ENT, false,
>                                         (struct vring_desc *)(uintptr_t)cvq->desc_addr,
>                                         (struct vring_avail *)(uintptr_t)cvq->driver_addr,
>                                         (struct vring_used *)(uintptr_t)cvq->device_addr);
>
> +               if (!err)
> +                       vringh_set_base_iotlb(&cvq->vring, last_avail_idx);
> +       }
>         return err;
>  }
>
> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> index 7b8fd977f71c..799762c83007 100644
> --- a/drivers/vhost/vringh.c
> +++ b/drivers/vhost/vringh.c
> @@ -595,6 +595,24 @@ static inline void __vringh_notify_disable(struct vringh *vrh,
>         }
>  }
>
> +static inline int __vringh_set_base(struct vringh *vrh, u16 idx,
> +                           int (*putu16)(const struct vringh *vrh,
> +                               __virtio16 *p, u16 val))
> +{
> +    int ret;
> +
> +    ret = putu16(vrh, &vrh->vring.avail->idx, idx);
> +    if (ret)
> +        return ret;
> +
> +    ret = putu16(vrh, &vrh->vring.used->idx, idx);
> +    if (ret)
> +        return ret;
> +

I don't think VMM should be able to modify the guest's vring memory.
For vringh it should be enough with the next line, no need for
previous.

If I'm not wrong this was solved in the simulator by [1] and [2]. Am I
missing something?

Thanks!

[1] https://lkml.org/lkml/2023/1/18/1045
[2] https://www.spinics.net/lists/kernel/msg4705724.html

> +    vrh->last_avail_idx = vrh->last_used_idx = idx;
> +    return 0;
> +}
> +
>  /* Userspace access helpers: in this case, addresses are really userspace. */
>  static inline int getu16_user(const struct vringh *vrh, u16 *val, const __virtio16 *p)
>  {
> @@ -1456,6 +1474,18 @@ void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
>  }
>  EXPORT_SYMBOL(vringh_set_iotlb);
>
> +/**
> + * vringh_set_base_iotlb - set avail_idx and used_idx
> + * @vrh: the vring
> + * @idx: the value to set
> + */
> +int vringh_set_base_iotlb(struct vringh *vrh, u16 idx)
> +{
> +    return __vringh_set_base(vrh, idx, putu16_iotlb);
> +}
> +EXPORT_SYMBOL(vringh_set_base_iotlb);
> +
> +
>  /**
>   * vringh_getdesc_iotlb - get next available descriptor from ring with
>   * IOTLB.
> diff --git a/include/linux/vringh.h b/include/linux/vringh.h
> index c3a8117dabe8..e9b8af4e6a5e 100644
> --- a/include/linux/vringh.h
> +++ b/include/linux/vringh.h
> @@ -306,6 +306,8 @@ int vringh_init_iotlb_va(struct vringh *vrh, u64 features,
>                          struct vring_avail *avail,
>                          struct vring_used *used);
>
> +int vringh_set_base_iotlb(struct vringh *vrh, u16 idx);
> +
>  int vringh_getdesc_iotlb(struct vringh *vrh,
>                          struct vringh_kiov *riov,
>                          struct vringh_kiov *wiov,
> --
> 2.39.3
>