Re: [PATCH] x86_32: trim memory by updating e820 v3

[Yinghai Lu]

On Mon, Apr 28, 2008 at 11:07 AM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> "Yinghai Lu" <yhlu.kernel@xxxxxxxxx> writes:
>
>  > On Sat, Apr 26, 2008 at 5:56 AM, Gabriel C <nix.or.die@xxxxxxxxxxxxxx> 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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