Re: IOMMU Query

[Joerg Roedel <joro@8bytes.org>]

On Wed, Mar 23, 2011 at 03:18:04PM -0700, Stepan Moskovchenko wrote:
> Consistency between multiple IOMMUs can be maintained. Map and unmap  
> operations happen on a 'domain' structure (which is intended to abstract  
> a page table), and a domain can be attached to one or more IOMMU  
> devices, assuming that all your IOMMUs use the same page table format.

The IOMMU-API even supports it if your IOMMUs have different page-table
formats. The driver can just setup page-tables in every possible format
on map/unmap and use the appropriate one for each device. So this is
possible if wanted.

> The IOMMU layer itself does not handle virtual space management. Its  
> sole responsibility is to set up the mappings. You would need something  
> else to do the management for you. There have been some discussions  
> about it in the past...

Which is by the way the point of the IOMMU-API. If you want address
space management done the the DMA-API is the better choice to implement
for your IOMMU. The DMA-API manages the address space itself.
Something was needed that allows the driver to manage the address space
itself (for KVM device passthrough). This was not possible with the
DMA-API so the IOMMU-API was introduced.
Your IOMMU driver can also implement both APIs like the x86 IOMMU
drivers do (VT-d and AMD-Vi).

Regards,

	Joerg