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

[Eric Auger <eauger@redhat.com>]

Hi Michael,

On 2/24/25 8:31 PM, Michael S. Tsirkin wrote:
> 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!
If I removed the line below, I hit the issue again:

qemu-system-aarch64: virtio: zero sized buffers are not allowed

So to me this is needed and the comment is right.

Eric
> 
>>> +	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)
>