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    SubjectRe: [PATCH 1/3] x86, intel: Output microcode revision

    * Andi Kleen <> wrote:

    > --- a/arch/x86/include/asm/processor.h
    > +++ b/arch/x86/include/asm/processor.h
    > @@ -111,6 +111,8 @@ struct cpuinfo_x86 {
    > /* Index into per_cpu list: */
    > u16 cpu_index;
    > #endif
    > + /* CPU update signature */
    > + u32 x86_cpu_update;

    Btw,. there's one subtle thing here: it's possible to have *different*
    microcode versions on different CPUs in te system.

    This can happen if for example the BIOS somehow does not apply the right
    microcode to all CPUs. It can also happen if physically different microcode
    version CPUs are mixed. In theory people can mix steppings as well.

    Would you be interested in adding a quick debugging check after all CPUs have
    been brought online, and print some very visible boot warning message if
    there's a mismatch between the steppings or microcode versions? Perhaps also
    taint the kernel.

    Having non-updated microcode is one thing, but having *mixed* versions can
    introduce its own set of problems: there are workarounds that have to be
    activated on all CPUs, otherwise the result may be undefined.

    We did not check for this before, so this would be a separate patch as well.

    This should be done in a generic way, so it should work with other x86 CPUs as



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