Hi Michael.
>> If the device then asks for VIRTIO_CONSOLE_F_DMA_MEM
>> when DMA is not supported, virtio will do BUG_ON() from
>> virtio_check_driver_offered_feature().
>>
>> Is this acceptable or should we add a check in virtcons_probe()
>> and let the probing fail instead?
>>
>> E.g:
>> /* Refuse to bind if F_DMA_MEM request cannot be met */
>> if (!VIRTIO_CONSOLE_HAS_DMA &&
>> (vdev->config->get_features(vdev) & (1 << VIRTIO_CONSOLE_F_DMA_MEM))){
>> dev_err(&vdev->dev,
>> "DMA_MEM requested, but arch does not support DMA\n");
>> err = -EINVAL;
>> goto fail;
>> }
>>
>> Regards,
>> Sjur
>
> Failing probe would be cleaner. But there is still a problem:
> old driver will happily bind to that device and then
> fail to work, right?
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.
> virtio pci has revision id for this, but remoteproc doesn't
> seem to have anything similar. Or did I miss it?
No there are currently no sanity check of
virtio type and feature bits in remoteproc.
One option may be to add this...
> If not -
> we probably need to use a different
> device id, and not a feature bit.
But if I create a new virtio console type, remoteproc
could still call the existing virtio_console with random
bad feature bits, causing kernel panic.
Even if we fix this particular problem, the general problem
still exists: bogus virtio declarations in remoteproc's firmware
may cause BUG_ON(). (Note the fundamental difference
between visualizations and remoteproc. For remoteproc
the virtio configuration comes from binaries loaded from
user space).
So maybe we should look for a more generic solution, e.g.
changing virtio probe functionality so that devices with
bad feature bits will not trigger BUG_ON(), but rather refuse
to bind the driver.
Regards,
Sjur
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