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    SubjectRe: [PATCH] Fix i486 suspend to disk CR4 oops
    Pavel Machek wrote:
    > Okay, can it happen that that cr4 is zero legitimately? If newer 486SX
    > chips support cr4 but not coprocessor...?
    > Pavel

    Theoretically it can, but that means no features are enabled, so there
    is no need to enable the features.

    The real question is if the following can happen: can it be such that we
    want CR4 to be zero in a situation where CR4 is nonzero to start out with?

    The main bit in CR4 that could be set that we wouldn't want set would be
    CR4.PAE, so this could happen if there is a CPU with CR4.PAE but none of
    the other CR4 bits that we would normally set unconditionally.

    I'm pretty sure this can't happen on any physical CPUs, since all
    physical CPUs supporting PAE would also support DE, MCE, and PGE. It
    could possibly happen on a virtual CPU, although it is of course
    extremely unlikely we'd get there with CR4 not zero to start out with.

    Still, it is at least theoretically wrong.


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