Re: [PATCH 06/11] virtio: blk: Add freeze, restore handlers to support S4

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

On Mon, Oct 03, 2011 at 02:46:46PM +0530, Amit Shah wrote:
> On (Sun) 02 Oct 2011 [11:37:33], Michael S. Tsirkin wrote:
> > On Thu, Sep 29, 2011 at 08:56:02PM +0530, Amit Shah wrote:
> > > Delete the vq on the freeze callback to prepare for hibernation.
> > > Re-create the vq in the restore callback to resume normal function.
> > > 
> > > Signed-off-by: Amit Shah <amit.shah@redhat.com>
> > > ---
> > >  drivers/block/virtio_blk.c |   17 +++++++++++++++++
> > >  1 files changed, 17 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > index 509760b..9844d2c 100644
> > > --- a/drivers/block/virtio_blk.c
> > > +++ b/drivers/block/virtio_blk.c
> > > @@ -549,6 +549,19 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
> > >  	kfree(vblk);
> > >  }
> > >  
> > > +#ifdef CONFIG_PM
> > > +static int virtblk_freeze(struct virtio_device *vdev)
> > > +{
> > > +	vdev->config->del_vqs(vdev);
> > 
> > What prevents the guest from trying to use the VQ while
> > this is in progress? IF it does, what prevents a crash?
> 
> An oversight: Sasha pointed this out, too, and I've now fixed this by
> adding a call to vdev->config->reset() before deleting vqs.
> 
> 		Amit

This stops the host from accessing the VQ, but does not stop the *guest*.