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

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Message-ID: <20240411134221.GL223006@ziepe.ca>
Date: Thu, 11 Apr 2024 10:42:21 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>, 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

On Thu, Apr 11, 2024 at 09:17:41PM +0800, Baolu Lu wrote:
> On 2024/4/11 7:14, Tian, Kevin wrote:
> > > 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.
> 
> Is NESTING_IOTLB more readable?

Yes

Jason