Re: [PATCH v2 3/4] iommu/hyperv: Add para-virtualized IOMMU support for Hyper-V guest

[Jacob Pan]

Hi Yu,

On Fri,  3 Jul 2026 00:05:17 +0800
Yu Zhang <zhangyu1@xxxxxxxxxxxxxxxxxxx> wrote:

> +static int hv_iommu_attach_dev(struct iommu_domain *domain, struct
> device *dev,
> +			       struct iommu_domain *old)
> +{
> +	u64 status;
> +	u32 prefix;
> +	unsigned long flags;
> +	struct pci_dev *pdev;
> +	struct hv_input_attach_device_domain *input;
> +	struct hv_iommu_endpoint *vdev = dev_iommu_priv_get(dev);
> +	struct hv_iommu_domain *hv_domain =
> to_hv_iommu_domain(domain);
> +	int ret;
> +
> +	if (vdev->hv_domain == hv_domain)
> +		return 0;
> +
Is this needed? seems the core code already skips same domain attach?
i.e.

static int __iommu_group_set_domain_internal(struct iommu_group *group,
					     struct iommu_domain
*new_domain, unsigned int flags)
{
...
	if (group->domain == new_domain)
		return 0;