[PATCH 01/34] AMD IOMMU: add Kconfig entry

Duran, Leo leo.duran at amd.com
Fri Jun 27 15:47:56 PDT 2008


On Friday, June 27, 2008 5:30 PM, Muli Ben-Yehuda wrote:

> > 2) IOMMU will not translate if the exclusion range has been enabled,
> and
> > the DMA address falls inside that range.
> > The exclusion range can be enabled for specific devices, or for all
> > devices... Enabling the exclusion range can be considered a
> 'performance
> > optimization' (no table-walks), with the caveat of not being able to
> > provide protection for devices sharing the exclusion range (BTW,
> there's
> > a single exclusion address range per IOMMU).
> 
> So, if I understand this correctly, could we implement Joerg's
> "almost-direct-map" by having 0-64MB translated for host-owned
> devices, and then 64MB-end excluded (again, for host-owned devices
> only)? If yes, it should provide a small boost in performance (may or
> may not be measurable) over having 64MB-end be an identity
> translation.
> 
> Cheers,
> Muli

Hi Muli,

Yes, you could set an exclusion range for addresses about the virtual
address space (or 'translation aperture').
I played with that in the context of "dma.ops" (not surprisingly, the
exclusion range was pretty busy!).

Again, keep in mind: no protection in the exclusion range (sort of
defeating the purpose of having an IOMMU in the first place), and only
ONE exclusion range per IOMMU.

Leo.





More information about the iommu mailing list