Re: [RFC 1/2] virtio_console: Add support for DMA memory allocation

Hi Michael.

quoted

Not just fail to work, the kernel will panic on the BUG_ON().
Remoteproc gets the virtio configuration from firmware loaded
from user space. So this type of problem might be triggered
for other virtio drivers as well.

how?

...

quoted

Even if we fix this particular problem, the general problem
still exists: bogus virtio declarations in remoteproc's firmware
may cause BUG_ON().

which BUG_ON exactly?

I am afraid I have been barking up the wrong tree here.
Please ignore my previous rambling about panics related
to device features.

I hit the  BUG() in virtio_check_driver_offered_feature():
First I did not declare the feature because DMA was not set:
static unsigned int features[] = {
...
#if VIRTIO_CONSOLE_HAS_DMA
	VIRTIO_CONSOLE_F_DMA_MEM,
#endif
};

and then in probe I checked if the feature was supported:
	    virtio_has_feature(vdev, VIRTIO_CONSOLE_F_DMA_MEM)

This triggered the BUG() in virtio_check_driver_offered_feature(),
because the driver was asking for a unknown-feature.

I can get avoid this by simply checking the devices feature bits directly
instead of using virtio_has_feature().

Regards,
Sjur