linux-kernel - Re: [PATCH v3 11/11] virtio: balloon: Add freeze, restore handlers to support S4

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Date:	Thu, 17 Nov 2011 15:03:46 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	levinsasha928@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 11/11] virtio: balloon: Add freeze, restore handlers
 to support S4

On Thu, Nov 17, 2011 at 05:59:20PM +0530, Amit Shah wrote:
> On (Thu) 17 Nov 2011 [14:25:08], Michael S. Tsirkin wrote:
> > On Thu, Nov 17, 2011 at 05:27:42PM +0530, Amit Shah wrote:
> > > Delete the vqs on the freeze callback to prepare for hibernation.
> > > Re-create the vqs in the restore callback to resume normal function.
> > > 
> > > Signed-off-by: Amit Shah <amit.shah@...hat.com>
> > > ---
> > >  drivers/virtio/virtio_balloon.c |   20 ++++++++++++++++++++
> > >  1 files changed, 20 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > > index 1ff3cf4..90149d1 100644
> > > --- a/drivers/virtio/virtio_balloon.c
> > > +++ b/drivers/virtio/virtio_balloon.c
> > > @@ -363,6 +363,22 @@ static void __devexit virtballoon_remove(struct virtio_device *vdev)
> > >  	kfree(vb);
> > >  }
> > >  
> > > +#ifdef CONFIG_PM
> > > +static int virtballoon_freeze(struct virtio_device *vdev)
> > > +{
> > > +	/* Now we reset the device so we can clean up the queues. */
> > > +	vdev->config->reset(vdev);
> > > +
> > 
> > This is a weird thing to do. We normally delete vqs then reset.
> 
> No, all the drivers first reset, then delete.


Interesting. I note that for PCI, reset actually just did an I/O
write, which in PCI is really posted, that is it
can complete on CPU before the device has received it.

Further, interrupts might have been pending on the CPU,
so device might get used after reset.

Patch coming.

-- 
MST
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