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

[Jean-Philippe Brucker]

On Mon, Jan 24, 2022 at 12:33:02PM -0400, Jason Gunthorpe wrote:
> 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@xxxxxxxxxxxxxxx>
> > > > 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?

Sure, if we can finalise the domains before attach that could also clean
up the drivers a bit.

Thanks,
Jean