Re: [PATCH] x86: introduce a new Linux defined feature flag for PAT support

[Andi Kleen <andi@firstfloor.org>]

Rene Herman wrote:
> On 08-05-08 12:19, Andi Kleen wrote:
> 
>>> Use a new Linux defined X86_FEATURE_PAT_GOOD feature flag to
>>
>> Better would be PAT_TESTED or PAT_RANDOMLY_APPROVED. Most of these
>> CPUs without PAT_GOOD have actually perfectly good PAT, as Windows
>> proves every day.
>>
>> The main flaw in all of this of course is that there is no procedure
>> to test CPUs which do not have the flag set yet.
> 
> Quite. And hiding the fact that the CPU _should_ have perfectly good
> PAT doesn't help any at all. The discussion turned into a mini-flame
> war enough that now noone would even consider backing down, but this
> current PAT setup just sucks plain and simple.

For old CPUs it is actually ok (after all they worked for years without
PAT), I just don't like it for new CPUs. It's a bad idea there and
in the x86 world it is a reasonable expectation that CPU features
generally work.

That said I am not aware of that many PAT erratas even on old CPUs.
There are a few, but they are known and well understood and could
well be black listed.

-Andi