Re: x86_64 IOMMU question

[Andi Kleen]

Boszormenyi Zoltan <zboszor@xxxxxxxxxxx> writes:

> is it possible to use the IOMMU to help 32 bit devices
> that limit their capabilities with pci_set_dma_mask()?
> E.g. the emu10k1 limits itself under 256MB. Can the IOMMU
> pass the data to/from the card from/to above 256MB?

It can only remap to the AGP aperture, which is usually
just below the 4GB boundary. In theory you could move the aperture
to a very low address and remap to that (see 
arch/x86_64/kernel/aperture.c), but that would waste memory.

-Andi

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