Re: [PATCH 1/1] x86: Exclude E820_RESERVED regions and memory holes above 4 GB from direct mapping.

[Jacob Shin <jacob.shin@amd.com>]

On Thu, 2011-10-20 at 16:30 -0500, H. Peter Anvin wrote:
> On 10/20/2011 02:28 PM, Andi Kleen wrote:
> > Jacob Shin <jacob.shin@amd.com> writes:
> > 
> >> On systems with very large memory (1 TB in our case), BIOS may report a
> >> reserved region or a hole in the E820 map, even above the 4 GB range. Exclude
> >> these from the direct mapping.
> > 
> > This doesn't make much sense.  Holes above 4GB are completely legal.
> > 
> > If you need to workaround a specific broken BIOS you would need a quirk
> > only matching that system, with a suitable "BIOS is broken" message.
> > 
> 
> The problem is that apparently right now we map those unconditionally
> into the 1:1 map and mark them cacheable in PAT, which we *don't* for
> the < 4 GiB map.
> 
> This thus makes the behavior match < 4 GiB, which is the correct
> behavior; this should be made clear in the patch description.

Will something like:

"On systems with very large memory (1 TB in our case), BIOS may report a
reserved region or a hole in the E820 map, even above the 4 GB range.
Avoid mapping them unconditionally into kernel 1:1 direct mapping as
cacheable memory, as we also already do for the MMIO hole under 4 GB."

Work?

Otherwise, does the patch look acceptable?

Thanks!

-Jacob Shin
Advanced Micro Devices, Inc.

> 
> 	-hpa
>