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    SubjectRe: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix task freezing failures

    On Mon, Oct 03, 2011 at 10:47:54AM +0200, Borislav Petkov wrote:
    > I think your patch makes sense because re-loading the ucode during
    > a suspend/resume cycle is unnecessary. If one wants to update the
    > microcode, it should happen later when the box is resumed again: you
    > simply put the new microcode image in /lib/firmware/... and on AMD
    > unload/reload the microcode module and on Intel you do either that or
    > use the deprecated microcode_ctl.

    I don't think it changes anything for suspend/resume cycles. They're
    different hooks. The proposed patch changes actual cpu hotplug paths.

    > However, let me test it on a couple of AMD boxes tomorrow to verify.
    > > At the moment I can't think of any clean solution that solves both these problems -
    > > a. The problem of requesting microcode from userspace when it is frozen (which can be individually
    > > solved by my patch).
    > > b. The possible need for a revised microcode during CPU online (due to the remote usecase of
    > > physically plugging-out and plugging-in a new CPU), when the tasks are frozen.
    > Yeah, let me remind you guys, we're talking about x86 CPUs here. AFAICT,
    > I don't think that physical unplug is supported by any vendor yet but
    > I'd welcome surprises :-).

    I recall hearing about someone experimenting with actual hotplug a
    while ago. Dunno whether that was production or not tho. Even if
    not, given the continuing penetration of x86 into highend, I don't
    think it would take too long to see physical CPU hotplug in
    production. Also, it just is a poor engineering.



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