Re: [dpdk-dev] [PATCH] vhost: Fix wrong handling of virtqueue array index

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Tue, Oct 27, 2015 at 08:24:00AM +0000, Xie, Huawei wrote:
> On 10/27/2015 3:52 PM, Tetsuya Mukawa wrote:
> > The patch fixes wrong handling of virtqueue array index when
> > GET_VRING_BASE message comes.
> > The vhost backend will receive the message per virtqueue.
> > Also we should call a destroy callback handler when both RXQ
> > and TXQ receives the message.
> >
> > Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
> > ---
> >  lib/librte_vhost/vhost_user/virtio-net-user.c | 20 ++++++++++----------
> >  1 file changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/lib/librte_vhost/vhost_user/virtio-net-user.c b/lib/librte_vhost/vhost_user/virtio-net-user.c
> > index a998ad8..99c075f 100644
> > --- a/lib/librte_vhost/vhost_user/virtio-net-user.c
> > +++ b/lib/librte_vhost/vhost_user/virtio-net-user.c
> > @@ -283,12 +283,10 @@ user_get_vring_base(struct vhost_device_ctx ctx,
> >  	struct vhost_vring_state *state)
> >  {
> >  	struct virtio_net *dev = get_device(ctx);
> > +	uint16_t base_idx = state->index / VIRTIO_QNUM * VIRTIO_QNUM;
> >  
> >  	if (dev == NULL)
> >  		return -1;
> > -	/* We have to stop the queue (virtio) if it is running. */
> > -	if (dev->flags & VIRTIO_DEV_RUNNING)
> > -		notify_ops->destroy_device(dev);
> Hi Tetsuya:
> I don't understand why we move it to the end of the function.
> If we don't tell the application to remove the virtio device from the

As you stated, he just moved it to the end of the function: it
still does invoke notfiy_ops->destroy_device() in the end.

And the reason he moved it to the end is he want to invoke the
callback just when the second GET_VRING_BASE message is received
for the queue pair. And while thinking twice, it's not necessary,
as we will do the "flags & VIRTIO_DEV_RUNNING" check first, it
doesn't matter on which virt queue we invoke the callback.


	--yliu

> data plane, then the vhost application is still operating on that
> device, we shouldn't do anything to the virtio_net device.
> For this case, as vhost doesn't use kickfd, it will not cause issue, but
> i think it is best practice firstly to remove it from data plan through
> destroy_device.
> 
> I think we could call destroy_device the first time we receive this
> message. Currently we don't have per queue granularity control to only
> remove one queue from data plane.
> 
> I am Okay to only close the kickfd for the specified queue index.
> 
> Btw, do you meet issue with previous implementation?
> >  
> >  	/* Here we are safe to get the last used index */
> >  	ops->get_vring_base(ctx, state->index, state);
> > @@ -300,15 +298,17 @@ user_get_vring_base(struct vhost_device_ctx ctx,
> >  	 * sent and only sent in vhost_vring_stop.
> >  	 * TODO: cleanup the vring, it isn't usable since here.
> >  	 */
> > -	if (dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd >= 0) {
> > -		close(dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd);
> > -		dev->virtqueue[state->index + VIRTIO_RXQ]->kickfd = -1;
> > -	}
> > -	if (dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd >= 0) {
> > -		close(dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd);
> > -		dev->virtqueue[state->index + VIRTIO_TXQ]->kickfd = -1;
> > +	if (dev->virtqueue[state->index]->kickfd >= 0) {
> > +		close(dev->virtqueue[state->index]->kickfd);
> > +		dev->virtqueue[state->index]->kickfd = -1;
> >  	}
> >  
> > +	/* We have to stop the queue (virtio) if it is running. */
> > +	if ((dev->flags & VIRTIO_DEV_RUNNING) &&
> > +			(dev->virtqueue[base_idx + VIRTIO_RXQ]->kickfd == -1) &&
> > +			(dev->virtqueue[base_idx + VIRTIO_TXQ]->kickfd == -1))
> > +		notify_ops->destroy_device(dev);
> > +
> >  	return 0;
> >  }
> >  
>