Re: [PATCH v3 06/10] iommu/amd: Reduce domain lock scope in attach device path

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2024/10/17 21:32, Jason Gunthorpe wrote:
> On Wed, Oct 16, 2024 at 05:34:57AM +0000, Vasant Hegde wrote:
>> Currently attach device path takes protection domain lock followed by
>> dev_data lock. Most of the operations in this function is specific to
>> device data except pdom_attach_iommu() where it updates protection
>> domain structure. Hence reduce the scope of protection domain lock.
>>
>> Note that this changes the locking order. Now it takes device lock
>> before taking domain lock (group->mutex -> dev_data->lock ->
>> pdom->lock). dev_data->lock is used only in device attachment path.
>> So changing order is fine. It will not create any issue.
>>
>> Finally move numa node assignment to pdom_attach_iommu().
> numa node assignment should only be done during domain
> allocation. This is important because the domain can be mapped prior
> to being attached and without the right nid table levels will be mis
> allocated.

Sorry for off the topic, just a question about the domain numa ID.

When a domain is about to be attached to a device on a different numa
node, what should the iommu driver do? Should it:

- Ignore the difference (probably log an informational message);

or

- Return -EINVAL to force the upper layer to allocate a different domain
   for the device?

Thanks,
baolu