Re: [RFC PATCH] virtio: (Partially) enable suspend/resume support

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

On Tue, Oct 05, 2010 at 07:15:31PM +0530, Amit Shah wrote:
> > > +
> > > +	spin_lock_irqsave(&vp_dev->lock, flags);
> > > +	list_for_each_entry(info, &vp_dev->virtqueues, node) {
> > > +		/* Select the queue we're interested in */
> > > +		iowrite16(info->queue_index,
> > > +			  vp_dev->ioaddr + VIRTIO_PCI_QUEUE_SEL);
> > > +
> > > +		/* Update the last idx we sent data in */
> > > +		iowrite16(virtqueue_get_avail_idx(info->vq),
> > > +			  vp_dev->ioaddr + VIRTIO_PCI_AVAIL_IDX);
> > 
> > Interesting. Could we just reset the ring instead?
> > I think this would also solve the qemu problem you
> > outline, won't it?
> 
> The problem here is qemu doesn't "know" we went into suspend and came
> out of it.  When going to suspend, qemu could've received a kick
> notification and would've been just about to process some queue entries.
> Now when we resume and reset the ring, qemu could crash anyway seeing
> invalid index values.

Hmm, I don't completely understand this.  When there's a reset I expect
this to discard any previous kicks. No?

>  I think that's happening now anyway.

How can one reproduce this?