Messages in this thread | | | Date | Thu, 20 Oct 2011 14:32:47 -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 02:30 PM, 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. >
Specifically, it's fine for them to be mapped; it's not fine for them to be mapped cacheable.
-hpa
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