Re: [PATCH 02/15] iommu: Introduce iommu domain types

Joerg Roedel
2015-01-30T12:22:38Z

Hi Will,

On Wed, Jan 28, 2015 at 02:19:34PM +0000, Will Deacon wrote:
> > +/* This are the possible domain-types */
> > +enum iommu_domain_type {
> > + IOMMU_DOMAIN_DMA, /* Domain used for DMA-API */
> > + IOMMU_DOMAIN_IDENTITY, /* Identity mapped domain */
>
> What happens if somebody calls map or unmap on an identity-mapping domain?
> Can we catch that in the IOMMU core before calling the IOMMU driver? That
> also implies we need something extra to parameterise the attributes for
> the mapping (e.g. cacheable, read-only) and also potentially the address
> range.

The domain type is only used by the IOMMU drivers to do be able to enter
special allocation paths (the AMD-Vi driver for example could allocate a
special internal domain type for IOMMU_DOMAIN_DMA).
But I think you are right, a couple of the current domain attributes we
have could be moved here, turning the domain-type into a bit-field. So
we could have bits for PAGING, CACHABLE, DMA_API and NESTING and build
the domain types above from those bits.

> > + IOMMU_DOMAIN_UNMANAGED, /* Domain mappings are managed by a third party
> > + user (like KVM or VFIO) */
>
> We already have the domain attributes (iommu_attr) to describe features
> of a domain. Is there really a need for this extra type, or can we extend
> the attribute set and allow for domain allocation with attributes?

I don't think that domains attributed will become obsolete with this
domain-type field. Some of the attributes should stay there for now,
like all the PAMU specific stuff. But I agree, some could be moved over.

Joerg