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

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Date: Mon, 8 Apr 2024 02:28:07 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, "Will
 Deacon" <will@...nel.org>, Robin Murphy <robin.murphy@....com>, "Jason
 Gunthorpe" <jgg@...pe.ca>
CC: "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: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Sunday, April 7, 2024 12:35 PM
> 
> On 4/6/24 8:55 PM, Baolu Lu wrote:
> >>
> >>> @@ -4607,10 +4623,11 @@ static void
> >>> intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
> >>>        */
> >>>       if (domain->type == IOMMU_DOMAIN_SVA) {
> >>>           intel_svm_remove_dev_pasid(dev, pasid);
> >>> +        cache_tag_unassign_domain(dmar_domain,
> >>> +                      FLPT_DEFAULT_DID, dev, pasid);
> >>
> >> is it correct to destroy the tag before teardown completes, e.g. iotlb
> >> still
> >> needs to be flushed in intel_pasid_tear_down_entry()?
> >
> > You are right. iotlb still needs to be there until the teardown
> > completes. I will investigate this more later.
> 
> I reviewed this again. Cache tags are designed specifically for mapping
> and unmapping paths. Therefore, there is no required order for attaching
> and detaching paths.
> 

Okay. intel_pasid_tear_down_entry() directly retrieves the information
from the pasid entry instead of relying on the domain cache tag info.
so yes destroying the tag at this point is fine.