Re: PCI-DMA: high address but no IOMMU - nForce4

["Marc Perkel" <marc@perkel.com>]

> On Fri, Oct 28, 2005 at 12:16:51AM +0200, Andi Kleen wrote:
>
> I will attach my own;  A brand new Amd64 dual-core thing.
> Works fine with  mem=2500M,  but blows up with  mem=3G  or
> without any override and full 4G complement in use.
>
> This board (ASUS A8N-SLI) does use NVIDIA nForce4 chipset with
> bios-option to map (hoist) "excess memory" out from first 4G to
> higher physical addresses so that it can be accessed by the
> processor.
>
> This board has no AGP at all in it, but it does have lots
> of PCIE, and a bit of PCI-X thrown in for "legacy cards".
> Somehow that detail breaks things when the machine really
> should use bounce-buffering, or something similar -- I don't
> know if Nvidia  nForce4 chipset does have IOMMU, though...
>
> If Nvidia did omit such essential piece of hardware from
> a modern chipset, I do find it amazingly short-sighted...
> (Of course they don't yield documentation of the chips to
> public so that I can't quickly verify this detail...)


For what it's worth I have almost the exact same hardware and got the same
error. Athlon X2 4400 with the same ASUS board. Reverting to 2.6.13.2
kernel works.