linux-kernel - Re: [patch 28/30] x86/microcode: Handle "offline" CPUs correctly

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Message-ID: <875y5kgqd4.ffs@tglx>
Date:   Sat, 12 Aug 2023 18:47:03 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        Ashok Raj <ashok.raj@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [patch 28/30] x86/microcode: Handle "offline" CPUs correctly

On Fri, Aug 11 2023 at 11:36, Thomas Gleixner wrote:
> On Thu, Aug 10 2023 at 22:46, Peter Zijlstra wrote:
> OTOH, it's not really required. Right now we mandate that _all_ present
> cores have at least one sibling online. For simplicity (and practical
> reasons - think "nosmt") we require the "primary" thread to be online.
>
> Microcode is strict per core, no matter how many threads are there. We
> would not need any of this mess if Intel would have synchronized the
> threads on microcode update like AMD does. This is coming with future
> CPUs which advertise "uniform" update with a scope ranging from core,
> package to systemwide.

Which still requires the "offline" CPU treatment as the siblings are not
allowed to sit in MWAIT or HLT. So this whole NMI exercise is bound to
stay.

Thanks,

        tglx