Re: [PATCH v2 2/6] x86, mm, pat: Change reserve_memtype() to handle WT

From: Toshi Kani
Date: Wed Sep 10 2014 - 16:41:30 EST


On Wed, 2014-09-10 at 13:14 -0700, H. Peter Anvin wrote:
> On 09/10/2014 12:30 PM, Toshi Kani wrote:
> >
> > When WT is unavailable due to the PAT errata, it does not fail but gets
> > redirected to UC-. Similarly, when PAT is disabled, WT gets redirected
> > to UC- as well.
> >
>
> But on pre-PAT hardware you can still do WT.

Yes, if we manipulates the bits directly, but such code is no longer
allowed for PAT systems. The PAT-based kernel interfaces won't work for
pre-PAT systems, and therefore requests are redirected to UC- on such
systems.

Thanks,
-Toshi

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