RE: [PATCH v2 02/10] iommu: Introduce a new iommu_group_replace_domain() API

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Wednesday, February 8, 2023 5:18 AM
> 
> +int iommu_group_replace_domain(struct iommu_group *group,
> +			       struct iommu_domain *new_domain)
> +{
> +	int ret;
> +
> +	if (!new_domain)
> +		return -EINVAL;
> +
> +	mutex_lock(&group->mutex);
> +	ret = __iommu_group_set_domain(group, new_domain);
> +	if (ret)
> +		__iommu_group_set_domain(group, group->domain);

Just realize the error unwind is a nop given below:

__iommu_group_set_domain()
{
	if (group->domain == new_domain)
		return 0;

	...

There was an attempt [1] to fix error unwind in iommu_attach_group(), by
temporarily set group->domain to NULL before calling set_domain().

Jason, I wonder why this recovering cannot be done in
__iommu_group_set_domain() directly, e.g.:

	ret = __iommu_group_for_each_dev(group, new_domain,
					  iommu_group_do_attach_device);
	if (ret) {
		__iommu_group_for_each_dev(group, group->domain,
					  iommu_group_do_attach_device);
		return ret;
	}
	group->domain = new_domain;

Thanks,
Kevin

[1] https://lore.kernel.org/linux-iommu/20230215052642.6016-1-vasant.hegde@xxxxxxx/