Re: PCI-DMA: Disabling IOMMU

[Muli Ben-Yehuda]

On Wed, Oct 18, 2006 at 05:51:57PM +0200, Sebastian Biallas wrote:
> Prakash Punnoor wrote:
> > Am Mittwoch 18 Oktober 2006 17:03 schrieben Sie:
> >> Linux ouputs some strange "PCI-DMA: Disabling IOMMU" on booting. It's a
> >> ALiveNF4G motherboard with an Athlon64 X2 running vanilla Linux 2.6.18.1
> >> (which supports all hardware out of the box, pretty cool).
> >>
> >> Should I worry about this IOMMU-disabling? All other Linux/IOMMU stuff I
> >> found had AGP or BIOS messages nearby, but I only get this single
> >> "PCI-DMA: Disabling IOMMU" line, without any hint.
> > 
> > Unless you have >=4GB of RAM using IOMMU makes no sense, thus it gets 
> > disabled.
> 
> Thanks for the answer (I thought that IOMMU is also used by VMMs like
> XEN, for direct hardware access of the guest. But I might have
> misunderstood this).

Nope, you got it right, that's one of the neater uses of an isolation
capable IOMMU.

Cheers,
Muli
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