Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces

Jean-Philippe Brucker
2018-05-17T10:02:42Z

On 17/05/18 00:31, Jacob Pan wrote:
> On Fri, 11 May 2018 20:06:04 +0100
> I am a little confused about domain vs. pasid relationship. If
> each domain represents a address space, should there be a domain for
> each pasid?

I don't think there is a formal definition, but from previous discussion
the consensus seems to be: domains are a collection of devices that have
the same virtual address spaces (one or many).

Keeping that definition makes things easier, in my opinion. Some time
ago, I did try to represent PASIDs using "subdomains" (introducing a
hierarchy of struct iommu_domain), but it required invasive changes in
the IOMMU subsystem and probably all over the tree.

You do need some kind of "root domain" for each device, so that
"iommu_get_domain_for_dev()" still makes sense. That root domain doesn't
have a single address space but a collection of subdomains. If you need
this anyway, representing a PASID with an iommu_domain doesn't seem
preferable than using a different structure (io_mm), because they don't
have anything in common.

Thanks,
Jean