Re: [PATCH] virtio: break and reset virtio devices on device_shutdown()

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

On Mon, Feb 24, 2025 at 08:49:09AM +0100, Eric Auger wrote:
> Hi Michael,
> 
> On 2/21/25 12:42 AM, Michael S. Tsirkin wrote:
> > Hongyu reported a hang on kexec in a VM. QEMU reported invalid memory
> > accesses during the hang.
> > 
> > 	Invalid read at addr 0x102877002, size 2, region '(null)', reason: rejected
> > 	Invalid write at addr 0x102877A44, size 2, region '(null)', reason: rejected
> > 	...
> > 
> > It was traced down to virtio-console. Kexec works fine if virtio-console
> > is not in use.
> > 
> > The issue is that virtio-console continues to write to the MMIO even after
> > underlying virtio-pci device is reset.
> > 
> > Additionally, Eric noticed that IOMMUs are reset before devices, if
> > devices are not reset on shutdown they continue to poke at guest memory
> > and get errors from the IOMMU. Some devices get wedged then.
> > 
> > The problem can be solved by breaking all virtio devices on virtio
> > bus shutdown, then resetting them.
> > 
> > Reported-by: Eric Auger <eauger@redhat.com>
> > Reported-by: Hongyu Ning <hongyu.ning@linux.intel.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Tested-by: Eric Auger <eric.auger@redhat.com>
> 
> Thanks!
> 
> Eric
> > ---
> >  drivers/virtio/virtio.c | 31 +++++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> > 
> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > index c1cc1157b380..e5b29520d3b2 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -377,6 +377,36 @@ static void virtio_dev_remove(struct device *_d)
> >  	of_node_put(dev->dev.of_node);
> >  }
> >  
> > +static void virtio_dev_shutdown(struct device *_d)
> > +{
> > +	struct virtio_device *dev = dev_to_virtio(_d);
> > +	struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
> > +
> > +	/*
> > +	 * Stop accesses to or from the device.
> > +	 * We only need to do it if there's a driver - no accesses otherwise.
> > +	 */
> > +	if (!drv)
> > +		return;
> > +
> > +	/*
> > +	 * Some devices get wedged if you kick them after they are
> > +	 * reset. Mark all vqs as broken to make sure we don't.
> > +	 */
> > +	virtio_break_device(dev);
> > +	/*
> > +	 * The below virtio_synchronize_cbs() guarantees that any interrupt
> > +	 * for this line arriving after virtio_synchronize_vqs() has completed
> > +	 * is guaranteed to see vq->broken as true.
> > +	 */
> > +	virtio_synchronize_cbs(dev);
> > +	/*
> > +	 * As IOMMUs are reset on shutdown, this will block device access to memory.
> > +	 * Some devices get wedged if this happens, so reset to make sure it does not.
> > +	 */

Eric,
Could you pls drop the below line (reset), and retest?
I want to make sure the above comment is right.
Thanks!

> > +	dev->config->reset(dev);


> > +}
> > +
> >  static const struct bus_type virtio_bus = {
> >  	.name  = "virtio",
> >  	.match = virtio_dev_match,
> > @@ -384,6 +414,7 @@ static const struct bus_type virtio_bus = {
> >  	.uevent = virtio_uevent,
> >  	.probe = virtio_dev_probe,
> >  	.remove = virtio_dev_remove,
> > +	.shutdown = virtio_dev_shutdown,
> >  };
> >  
> >  int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)