linux-kernel - Re: [PATCH v1 1/2] x86/cpufeature: Add facility to match microcode revisions

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Date:   Sat, 6 Oct 2018 20:39:28 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, peterz@...radead.org,
        x86@...nel.org, linux-kernel@...r.kernel.org, eranian@...gle.com,
        kan.liang@...el.com, isaku.yamahata@...el.com, kvm@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v1 1/2] x86/cpufeature: Add facility to match microcode
 revisions

On Sat, Oct 06, 2018 at 11:15:07AM -0700, Andi Kleen wrote:
> The matcher can be used to match specific hardware steppings by setting
> the min/max_ucode to 0 or specific microcode revisions 
> (which are associated with steppings)

This better be explained unambiguously.

> We still support the old microcode interface that allows updates
> per CPU, and also it could happen during CPU hotplug.

There are no per CPU microcode updates anymore - it is all or none.

It is actually your microcoders who came up with a bunch of restrictions
like quiescing the cores from doing *anything*, blocking hotplug,
prohibiting updates if a subset of the cores is not online and still not
guaranteeing it'll work all the time because <reasons>.

The actually very simple reason being it is just too late for microcode
update when the machine is up. Where all I wanna do is rip the damn
thing out completely.

-- 
Regards/Gruss,
    Boris.

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