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    SubjectRe: [RFC PATCH 02/12] PAT 64b: Basic PAT implementation
    > I do know we need to use the low 4 pat mappings to avoid most of the PAT
    > errata issues.

    They don't really matter. These are all very old systems who have run
    fine for many years without PAT. It is no problem to let them
    continue to do so and just disable PAT for them. So just clear pat bit in
    CPU initialization for any CPUs with non trivial erratas in this

    PAT is only really needed on modern boxes.

    Just someone needs to go through the old errata sheets and find
    out on which CPUs it is needed to clear the bit.

    > As for Andi's concern about modules playing games with the PAT mappings
    > if we don't redefine how we use the page table entries our exposure to
    > badly behaved modules more limited.

    I would just recheck them after module load and if it happens
    print a nasty message and program them back. e.g. kernel debuggers
    need an after module notifier anyways, so it would be fine
    to just add one and hook into that.


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