Re: Question about iommu on x86_64 and radeon driver.

[Daniel Haid]

> > I see. Now, maybe this will not work for some reason, but
> > would it be possible to somehow disable both IOMMU and SWIOTLB
> > and tell all drivers only to do DMA with the lower 4GB of memory?
>
> Only if you allow 3GB or less in the machine. So you would have to do
> mem=3G as well.
>
> The reason is that (and you can see that yourself by looking at the
> E820), is that 1GB is actually _above_ the 4GB.

I see. Is it possible to somehow give "mem=3G" to the kernel and still
use the memory above 4G for something, like a ramdisk or something?
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