Re: [PATCH v1] vhost: fail device start if iotlb update fails

[Jason Wang]

Hi Prasad:

On Thu, Nov 7, 2024 at 7:33 PM Prasad Pandit <ppandit@redhat.com> wrote:
>
> From: Prasad Pandit <pjp@fedoraproject.org>
>
> While starting a vhost device, updating iotlb entries
> via 'vhost_device_iotlb_miss' may return an error.
>
>   qemu-kvm: vhost_device_iotlb_miss:
>     700871,700871: Fail to update device iotlb

Actually, such updating is a workaround for vhost-net kernel to run.

I wonder what kind of issue would we get if we don't do this?

Thanks

>
> Fail device start when such an error occurs.
>
> Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
> ---
>  hw/virtio/vhost.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> v1:
>  - Remove VHOST_OPS_DEBUG call.
>  - Call vhost_set_iotlb_callback and vhost_dev_start with 'false' argument.
>
> v0:
>  - 
> 20241105060053.61973-1-ppandit@redhat.com/">https://lore.kernel.org/qemu-devel/20241105060053.61973-1-ppandit@redhat.com/
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 76f9b2aaad..c40f48ac4d 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -2095,11 +2095,22 @@ int vhost_dev_start(struct vhost_dev *hdev, 
> VirtIODevice *vdev, bool vrings)
>           * vhost-kernel code requires for this.*/
>          for (i = 0; i < hdev->nvqs; ++i) {
>              struct vhost_virtqueue *vq = hdev->vqs + i;
> -            vhost_device_iotlb_miss(hdev, vq->used_phys, true);
> +            r = vhost_device_iotlb_miss(hdev, vq->used_phys, true);
> +            if (r) {
> +                goto fail_iotlb;
> +            }
>          }
>      }
>      vhost_start_config_intr(hdev);
>      return 0;
> +fail_iotlb:
> +    if (vhost_dev_has_iommu(hdev) &&
> +        hdev->vhost_ops->vhost_set_iotlb_callback) {
> +        hdev->vhost_ops->vhost_set_iotlb_callback(hdev, false);
> +    }
> +    if (hdev->vhost_ops->vhost_dev_start) {
> +        hdev->vhost_ops->vhost_dev_start(hdev, false);
> +    }
>  fail_start:
>      if (vrings) {
>          vhost_dev_set_vring_enable(hdev, false);
> --
> 2.47.0
>