Messages in this thread | | | Date | Wed, 08 May 2013 15:49:02 -0700 | From | "H. Peter Anvin" <> | Subject | Re: WT memory type on x86_64? |
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On 05/08/2013 09:37 AM, Andy Lutomirski wrote: >> >> Not sure whether this is the reason but UC and UC- (as well as WB) are kept like >> the backward compatible setup. So for systems with and without PAT cache types >> map to the same. Only WT gets replaced by WC. For that whenever PCD is set it >> means some uncached type. > > This also makes the pgprot_xyz macros faster -- they can do the same > thing regardless of PAT settings. >
It also deals with errata in some very old CPUs... old enough that we don't use PAT on them anyway AFAIK.
-hpa
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