linux-kernel - RE: [PATCH v2 12/12] iommu/vt-d: Retire struct intel

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Date: Thu, 11 Apr 2024 08:32:11 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, Jason Gunthorpe <jgg@...pe.ca>
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 v2 12/12] iommu/vt-d: Retire struct intel_svm

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Thursday, April 11, 2024 3:56 PM
> 
> On 2024/4/10 23:49, Jason Gunthorpe wrote:
> > On Wed, Apr 10, 2024 at 10:08:44AM +0800, Lu Baolu wrote:
> >> @@ -4388,14 +4386,8 @@ static void
> intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
> >>   	WARN_ON_ONCE(!dev_pasid);
> >>   	spin_unlock_irqrestore(&dmar_domain->lock, flags);
> >>
> >> -	/*
> >> -	 * The SVA implementation needs to handle its own stuffs like the
> mm
> >> -	 * notification. Before consolidating that code into iommu core, let
> >> -	 * the intel sva code handle it.
> >> -	 */
> >>   	if (domain->type == IOMMU_DOMAIN_SVA) {
> >>   		cache_tag_unassign_domain(dmar_domain,
> FLPT_DEFAULT_DID, dev, pasid);
> >> -		intel_svm_remove_dev_pasid(domain);
> >>   	} else {
> >>   		did = domain_id_iommu(dmar_domain, iommu);
> >>   		cache_tag_unassign_domain(dmar_domain, did, dev, pasid);
> >
> > It seems very strange that SVA has a different DID scheme, why is
> > this? PASID and SVA should not be different at this layer.
> 
> The VT-d spec recommends that all SVA domains share a single domain ID.
> The PASID is unique to each SVA domain, hence the cache tags are unique.
> Currently, the Intel IOMMU driver assigns different domain IDs for all
> domains except the SVA type.
> 
> Sharing a domain ID is not specific to SVA. In general, for devices
> under a single IOMMU, domains with unique PASIDs can share the same
> domain ID.
> 
> In the long term (also on my task list), we will extend the cache tag
> code to support sharing domain IDs and remove the domain type check from
> the main code. This will also benefit the nesting case, where user
> domains nested on the same parent could share a domain ID.
> 

at least above might be changed to a unified call with the helper
accepting an iommu parameter and then finding proper did
internally based on domain type, e.g.

cache_tag_unassign_domain(domain, iommu, dev, pasid)
{
	if (domain->type == IOMMU_DOMAIN_SVA)
		did = FLPT_DEFAULT_DID;
	else
		did = domain_id_iommu(domain, iommu);

	...
}