linux-kernel - RE: [PATCH 01/12] iommu/vt-d: Add cache tag assignment interface

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Date: Wed, 10 Apr 2024 23:14:30 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Lu Baolu <baolu.lu@...ux.intel.com>
CC: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, "Robin
 Murphy" <robin.murphy@....com>, "Zhang, Tina" <tina.zhang@...el.com>, "Liu,
 Yi L" <yi.l.liu@...el.com>, "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 01/12] iommu/vt-d: Add cache tag assignment interface

> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Wednesday, April 10, 2024 11:42 PM
> 
> On Mon, Mar 25, 2024 at 10:16:54AM +0800, Lu Baolu wrote:
> > +static int __cache_tag_assign_parent_domain(struct dmar_domain
> *domain, u16 did,
> > +					    struct device *dev, ioasid_t pasid)
> > +{
> > +	struct device_domain_info *info = dev_iommu_priv_get(dev);
> > +	int ret;
> > +
> > +	ret = cache_tag_assign(domain, did, dev, pasid,
> CACHE_TAG_TYPE_PARENT_IOTLB);
> > +	if (ret || !info->ats_enabled)
> > +		return ret;
> 
> I'm not sure I understood the point of PARENT_IOTLB? I didn't see any
> different implementation?
> 
> Isn't this backwards though? Each domain should have a list of things
> to invalidate if the domain itself changes.
> 
> So the nesting parent should have a list of CHILD_DEVTLB's that need
> cleaning. That list is changed when the nesting domains are attached
> to something.
> 

probably just a naming confusion. it's called PARENT_IOTLB from the
angle that this domain is used as a parent domain but actually it
tracks the child tags in nested attach.