Re: [PATCH v2 12/12] iommu/vt-d: Retire struct intel_svm

[Baolu Lu]

On 2024/4/11 16:32, Tian, Kevin wrote:
> > From: Baolu Lu<baolu.lu@xxxxxxxxxxxxxxx>
> > 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);
>
> 	...
> }

Yeah, your code is more graceful.

Best regards,
baolu