Re: [PATCH] hw/virtio: propagate vhost_virtqueue_mask() errors from start path

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jun 04, 2026 at 08:44:20PM +0800, Bin Guo wrote:
> vhost_virtqueue_start() unmasks the call notifier by calling
> vhost_virtqueue_mask(), whose vhost_set_vring_call ioctl can fail
> (closed vhost-user socket, kernel ENOMEM, revoked guest_notifier fd)
> but whose void signature throws the error away. vhost_dev_start()
> then reports success while the backend has no valid call eventfd for
> that vq, leaving the guest with a working kick path but no virtqueue
> interrupts -- a half-up state harder to diagnose than a clean failure.
> 
> Make vhost_virtqueue_mask() return int and handle the error in the
> start path via the existing fail_vector unwind. Other callers reach
> the function through VirtioDeviceClass.guest_notifier_mask, whose
> void signature offers no upward error channel; they invoke it as a
> statement and remain source-compatible.
> 
> Resolves a long-standing TODO at the unmask call.
> 
> Signed-off-by: Bin Guo <guobin@linux.alibaba.com>
> ---
>  hw/virtio/vhost.c         | 12 +++++++++---
>  include/hw/virtio/vhost.h |  4 ++--
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index b9dc4ed13b..42e2fc9952 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1351,8 +1351,11 @@ int vhost_virtqueue_start(struct vhost_dev *dev,
>       * will do it later.
>       */
>      if (!vdev->use_guest_notifier_mask) {
> -        /* TODO: check and handle errors. */
> -        vhost_virtqueue_mask(dev, vdev, idx, false);
> +        r = vhost_virtqueue_mask(dev, vdev, idx, false);
> +        if (r < 0) {
> +            /* No call eventfd means no interrupts; bail out. */
> +            goto fail_vector;
> +        }
>      }
>  
>      if (k->query_guest_notifiers &&



Can you rebase please? Thanks!

> @@ -1815,7 +1818,7 @@ bool vhost_virtqueue_pending(struct vhost_dev *hdev, int n)
>  }
>  
>  /* Mask/unmask events from this vq. */
> -void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
> +int vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
>                           bool mask)
>  {
>      struct VirtQueue *vvq = virtio_get_queue(vdev, n);
> @@ -1836,7 +1839,10 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
>      r = hdev->vhost_ops->vhost_set_vring_call(hdev, &file);
>      if (r < 0) {
>          error_report("vhost_set_vring_call failed %d", -r);
> +        return r;
>      }
> +
> +    return 0;
>  }
>  
>  bool vhost_config_pending(struct vhost_dev *hdev)
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 89817bd848..96cc261822 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -317,8 +317,8 @@ bool vhost_virtqueue_pending(struct vhost_dev *hdev, int n);
>  
>  /* Mask/unmask events from this vq.
>   */
> -void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
> -                          bool mask);
> +int vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
> +                         bool mask);
>  
>  /**
>   * vhost_get_features_ex() - sanitize the extended features set
> -- 
> 2.50.1 (Apple Git-155)