Messages in this thread | | | Date | Thu, 20 Oct 2011 14:30:05 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 1/1] x86: Exclude E820_RESERVED regions and memory holes above 4 GB from direct mapping. |
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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.
-hpa
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