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

Tian, Kevin
2022-07-07T06:31:37Z

> From: Robin Murphy <robin.murphy@arm.com>
> 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.