Re: [PATCH net-next 2/3] vhost: introduce vhost_vq_more_avail()

Michael S. Tsirkin
2015-11-30T08:22:09Z

On Wed, Nov 25, 2015 at 03:11:28PM +0800, Jason Wang wrote:
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> drivers/vhost/vhost.c | 26 +++++++++++++++++---------
> drivers/vhost/vhost.h | 1 +
> 2 files changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 163b365..b86c5aa 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1633,10 +1633,25 @@ void vhost_add_used_and_signal_n(struct vhost_dev *dev,
> }
> EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);
>
> +bool vhost_vq_more_avail(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> +{
> + __virtio16 avail_idx;
> + int r;
> +
> + r = __get_user(avail_idx, &vq->avail->idx);
> + if (r) {
> + vq_err(vq, "Failed to check avail idx at %p: %d\n",
> + &vq->avail->idx, r);
> + return false;

In patch 3 you are calling this under preempt disable,
so this actually can fail and it isn't a VQ error.

> + }
> +
> + return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx;
> +}
> +EXPORT_SYMBOL_GPL(vhost_vq_more_avail);
> +
> /* OK, now we need to know about added descriptors. */
> bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> {
> - __virtio16 avail_idx;
> int r;
>
> if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
> @@ -1660,14 +1675,7 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> /* They could have slipped one in as we were doing that: make
> * sure it's written, then check again. */
> smp_mb();
> - r = __get_user(avail_idx, &vq->avail->idx);
> - if (r) {
> - vq_err(vq, "Failed to check avail idx at %p: %d\n",
> - &vq->avail->idx, r);
> - return false;
> - }
> -
> - return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx;
> + return vhost_vq_more_avail(dev, vq);
> }
> EXPORT_SYMBOL_GPL(vhost_enable_notify);
>

This path does need an error though.
It's probably easier to just leave this call site alone.

> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 43284ad..2f3c57c 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -159,6 +159,7 @@ void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
> struct vring_used_elem *heads, unsigned count);
> void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
> void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
> +bool vhost_vq_more_avail(struct vhost_dev *, struct vhost_virtqueue *);
> bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
>
> int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
> --
> 2.5.0