Re: [PATCH v3 03/15] iommu: Always register bus notifiers

[Robin Murphy]

On 2022-07-07 07:31, Tian, Kevin wrote:
> > From: Robin Murphy <robin.murphy@xxxxxxx>
> > Sent: Wednesday, July 6, 2022 1:08 AM
> >
> > The number of bus types that the IOMMU subsystem deals with is small and
> > manageable, so pull that list into core code as a first step towards
> > cleaning up all the boilerplate bus-awareness from drivers. Calling
> > iommu_probe_device() before bus->iommu_ops is set will simply return
> > -ENODEV and not break the notifier call chain, so there should be no
> > harm in proactively registering all our bus notifiers at init time.
>
> Suppose we miss a check on iommu ops in iommu_release_device():
>
> 	if (!dev->iommu) <<<<<<<
> 		return;
>
> 	iommu_device_unlink(dev->iommu->iommu_dev, dev);
>
> 	ops = dev_iommu_ops(dev);
> 	ops->release_device(dev);
>
> following the rationale in patch01 a device could be removed when
> it's associated with a known but not registered instance.

No, because at that point the instance is only known internally to the 
driver. As long as it isn't erroneously returned from 
->probe_device(dev), dev->iommu will remain NULL and the rest of the 
core code works as expected.

Thanks,
Robin.