Re: [PATCH 7/7] iommu: Add iommu_domain::domain_ops

[Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>]

On Mon, Jan 24, 2022 at 10:16:07AM +0000, Jean-Philippe Brucker wrote:
> On Mon, Jan 24, 2022 at 09:58:18AM +0000, Tian, Kevin wrote:
> > > From: Lu Baolu <baolu.lu@linux.intel.com>
> > > Sent: Monday, January 24, 2022 3:11 PM
> > > +/**
> > > + * struct domain_ops - per-domain ops
> > > + * @attach_dev: attach an iommu domain to a device
> > > + * @detach_dev: detach an iommu domain from a device
> > 
> > What is the criteria about whether an op should be iommu_ops or domain_ops
> > when it requires both domain and device pointers like above two (and future
> > PASID-based attach)?
> > 
> > Other examples include:
> > 	@apply_resv_region
> > 	@is_attach_deferred
> 
> Could attach_dev() be an IOMMU op?  So a driver could set the domain ops
> in attach_dev() rather than domain_alloc(). That would allow to install
> map()/unmap() ops that are tailored for the device's IOMMU, which we don't
> know at domain_alloc() time. 

I think we should be moving toward 'domain_alloc' returning the
correct domain and the way the driver implements the domain shouldn't
change after that.

> I'm thinking about a guest that has both physical and virtual
> endpoints, which would ideally use different kinds of domain ops to
> support both efficiently (caching mode vs page tables)

In this case shouldn't domain_alloc() reached from the struct device
already do the correct thing?

Jason
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