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    SubjectRe: [PATCH 4/7] x86/microcode: Do not upload microcode if CPUs are offline
    On Wed, 28 Feb 2018, Borislav Petkov wrote:
    > Avoid loading microcode if any of the CPUs are offline, and issue a
    > warning. Having different microcode revisions on the system at any time
    > is outright dangerous.

    Even if we update that microcode during CPU early bring-up, before we
    mark it on-line and start using it?

    AFAIK, late-loading or not, this is what should happen in the current
    code: APs that are brought up after a microcode update is loaded (either
    by the early or late driver, it doesn't matter) will be always
    *early-updated* to the new microcode.

    Is it dangerous to have an offline core at an older microcode revision
    than the online cores?

    I am not against the patch, mind you, but I am curious about why it is
    supposed to be dangerous if we're updating the CPUs before we start
    using them *anyway*.

    Also, if this is really dangerous, does it means safe CPU hotplug isn't
    possible? AFAICT, the firmware would have to do it for us, but it
    *doesn't* have the up-to-date microcode (*we* had to update it)...

    --
    Henrique Holschuh

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