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Date: Thu, 3 Feb 2011 12:25:05 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Yinghai Lu <yinghai@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>, David Miller <davem@davemloft.net>,
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        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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Subject: Re: [PATCH - resend] memblock: Don't adjust size in
 memblock_find_base()
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On Fri, 28 Jan 2011 16:37:47 -0800
Yinghai Lu <yinghai@kernel.org> wrote:

> 
> While applying patch to use memblock to find aperture for 64bit x86.
> Ingo found system with 1g + force_iommu
> 
> > No AGP bridge found
> > Node 0: aperture @ 38000000 size 32 MB
> > Aperture pointing to e820 RAM. Ignoring.
> > Your BIOS doesn't leave a aperture memory hole
> > Please enable the IOMMU option in the BIOS setup
> > This costs you 64 MB of RAM
> > Cannot allocate aperture memory hole (0,65536K)

I'm trying to work out if we should backport this fix into earlier
kernels and as is often the case, I wasn't given enough information.

What are the end-user visible effects of this?  The kernel cannot use
the AGP bridge?  64MB of RAM wasted?  Something else?