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    SubjectRe: [patch 00/37] cpu/hotplug, x86: Reworked parallel CPU bringup
    On Sat, Apr 15, 2023 at 01:44:13AM +0200, Thomas Gleixner wrote:

    > Background
    > ----------
    >
    > The reason why people are interested in parallel bringup is to shorten
    > the (kexec) reboot time of cloud servers to reduce the downtime of the
    > VM tenants. There are obviously other interesting use cases for this
    > like VM startup time, embedded devices...

    ...

    > There are two issue there:
    >
    > a) The death by MCE broadcast problem
    >
    > Quite some (contemporary) x86 CPU generations are affected by
    > this:
    >
    > - MCE can be broadcasted to all CPUs and not only issued locally
    > to the CPU which triggered it.
    >
    > - Any CPU which has CR4.MCE == 0, even if it sits in a wait
    > for INIT/SIPI state, will cause an immediate shutdown of the
    > machine if a broadcasted MCE is delivered.

    When doing kexec, CR4.MCE should already have been set to 1 by the prior
    kernel, no?

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