Subject: Re: [RFC V4 PATCH 7/8] vhost: packed ring support

From: Wei Xu <[email-masked]>
Date: Wed, 23 May 2018 00:54:48 +0800

On Wed, May 16, 2018 at 08:32:20PM +0800, Jason Wang wrote:
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/vhost/net.c   |   3 +-
>  drivers/vhost/vhost.c | 539 ++++++++++++++++++++++++++++++++++++++++++++++----
>  drivers/vhost/vhost.h |   8 +-
>  3 files changed, 513 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 8304c30..f2a0f5b 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1358,6 +1382,8 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
>  			break;
>  		}
>  		vq->last_avail_idx = s.num;
> +		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
> +			vq->avail_wrap_counter = s.num >> 31;
>  		/* Forget the cached index value. */
>  		vq->avail_idx = vq->last_avail_idx;
>  		break;
> @@ -1366,6 +1392,8 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
>  		s.num = vq->last_avail_idx;
>  		if (copy_to_user(argp, &s, sizeof s))
>  			r = -EFAULT;
> +		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
> +			s.num |= vq->avail_wrap_counter << 31;
>  		break;
>  	case VHOST_SET_VRING_ADDR:
>  		if (copy_from_user(&a, argp, sizeof a)) {

'last_used_idx' also needs to be saved/restored here.

I have figured out the root cause of broken device after reloading
'virtio-net' module, all indices have been reset for a reloading but
'last_used_idx' is not properly reset in this case. This confuses
handle_rx()/tx().

Wei