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



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