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SubjectRe: [PATCH] x86_32: trim memory by updating e820 v3
On Mon, Apr 28, 2008 at 11:07 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> "Yinghai Lu" <yhlu.kernel@gmail.com> writes:
>
> > On Sat, Apr 26, 2008 at 5:56 AM, Gabriel C <nix.or.die@googlemail.com> wrote:
>
>
> > another continuous MTRR mapping.
> >
> > several months ago, we were talking about modifying MTRR. but Eric
> > said that is not safe because acpi and smi...
>
> I think it was Andi who spotted that originally, and yes I do think it
> is a pretty horrific failure mode. Reprogramming the MTRRs requires
> full knowledge of the hardware and what is going on that we don't
> always have. PAT support has just been merged, and using that only
> requires knowledge about the region whose attributes we intend to change.
>
> So lets concentrate on PAT to solve contiguous MTRR region problems.
>
> We can upgrade UC to WC with pat. As well as demote WB to UC or WC.
> So for those regions we know about we should be in good shape.
>
> In a slightly related vein. Trimming the memory we consider usable by
> looking at MTRRs and if a region is not WB not considering it RAM
> sounds like a very reasonable work around for one class of BIOS bugs.

yeah, i will look at to loop the ram region array instead of checking
highest_pfn only...


YH


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