Re: [PATCH] trim memory not covered by WB MTRRs

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Tuesday, June 26, 2007 8:03:48 am Andi Kleen wrote:
> On Mon, Jun 25, 2007 at 08:30:52PM -0700, Jesse Barnes wrote:
> > Oh, and FYI I've seen new systems with a default mapping type of WB, with
> > a few uncached holes for MMIO.  That means PAT will be absolutely
> > required on those systems if we want to use WC for the framebuffer or
> > other memory.
>
> Why? As long as there are still MTRRs free you could use them for
> WC even in this setup.

According to the manual, you can't use WC or WT MTRRs on top of a WB MTRR 
range.  Only UC MTRRs can override WB MTRRs, but PAT doesn't have this 
restriction.

Jesse