Re: [PATCH] virtio: Remove virtio devices on device_shutdown()

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

On Thu, Aug 08, 2024 at 10:51:41AM +0300, Kirill A. Shutemov 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.

virtio is not doing a lot of 16 bit reads.
Are these the reads:

                virtio_cread(vdev, struct virtio_console_config, cols, &cols);
                virtio_cread(vdev, struct virtio_console_config, rows, &rows);

?

write is a bit puzzling too. This one?

bool vp_notify(struct virtqueue *vq)
{       
        /* we write the queue's selector into the notification register to
         * signal the other end */
        iowrite16(vq->index, (void __iomem *)vq->priv);
        return true;
}
        
> 
> Looks like virtio-console continues to write to the MMIO even after
> underlying virtio-pci device is removed.

You mention both MMIO and pci, I am confused.
Removed by what? In what sense?




> 
> The problem can be mitigated by removing all virtio devices on virtio
> bus shutdown.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reported-by: Hongyu Ning <hongyu.ning@linux.intel.com>

A bit worried about doing so much activity on shutdown,
and for all devices, too. I'd like to understand what
is going on a bit better - could be a symptom of
a bigger problem (e.g. missing handling for suprise
removal?).




> ---
>  drivers/virtio/virtio.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index a9b93e99c23a..6c2f908eb22c 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -356,6 +356,15 @@ 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);
> +
> +	if (drv && drv->remove)
> +		drv->remove(dev);
> +}
> +
>  static const struct bus_type virtio_bus = {
>  	.name  = "virtio",
>  	.match = virtio_dev_match,
> @@ -363,6 +372,7 @@ 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)
> -- 
> 2.43.0