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

Robin Murphy
2022-07-07T09:59:06Z

On 2022-07-07 07:31, Tian, Kevin wrote:
>> 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.

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.