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

[Duran, Leo]

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.



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