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    SubjectRe: Fail to early boot with v2.6.27-rc2 to at least v2.6.29-rc2 due to dc1e35c
    Suresh Siddha wrote:
    > On Mon, Jan 19, 2009 at 02:07:36PM -0800, H. Peter Anvin wrote:
    >> Suresh Siddha wrote:
    >>> Also, I wonder, if we should complain/scream during boot if we find only
    >>> fewer cpuid levels on modern generation cpu's.
    >>>
    >> We should, or if this block is reversible, we should probably just undo
    >> it (the reason people put this block in places is because of, ahem,
    >> inferior operating systems having bugs.)
    >>
    >> Do you know how this is managed? Via an MSR?
    >
    > IA32_MISC_ENABLE MSR bit 22

    LOL, the official name of this bit is "IA32_MISC_ENABLES.BOOT_NT4"; kind
    of says it all. In fact, I remember the problems we had with NT4 and
    CPUID back from the Transmeta days, and there, too, we ended up with a
    CPUID hack which Linux unconditionally disables.

    I'll write up a patch.

    -hpa





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