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Date: Wed, 8 Jul 2026 18:55:35 +0800
From: Yu Zhang <zhangyu1@linux.microsoft.com>
To: Jacob Pan <jacob.pan@linux.microsoft.com>
Cc: linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, 
	iommu@lists.linux.dev, linux-pci@vger.kernel.org, linux-arch@vger.kernel.org, 
	wei.liu@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com, 
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	tgopinath@linux.microsoft.com, easwar.hariharan@linux.microsoft.com, 
	mrathor@linux.microsoft.com
Subject: Re: [PATCH v2 3/4] iommu/hyperv: Add para-virtualized IOMMU support
 for Hyper-V guest
Message-ID: <t7ghdzre3gbxgfu2d7jt2hc6ktofm3n5ifvzzjmh6wzlqlbrv6@bzyl3xepeith>
References: <20260702160518.311234-1-zhangyu1@linux.microsoft.com>
 <20260702160518.311234-4-zhangyu1@linux.microsoft.com>
 <20260706095510.00007ce1@linux.microsoft.com>
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In-Reply-To: <20260706095510.00007ce1@linux.microsoft.com>

On Mon, Jul 06, 2026 at 09:55:10AM -0700, Jacob Pan wrote:
> Hi Yu,
> 
> On Fri,  3 Jul 2026 00:05:17 +0800
> Yu Zhang <zhangyu1@linux.microsoft.com> 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;
> 

Thanks for catching this, Jacob. Will remove

B.R.
Yu