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

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Date:   Fri, 11 Aug 2023 03:19:27 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [patch 28/30] x86/microcode: Handle "offline" CPUs correctly

On Thu, Aug 10 2023 at 16:02, Ashok Raj wrote:
> On Fri, Aug 11, 2023 at 12:29:57AM +0200, Peter Zijlstra wrote:
>> 
>> Yeah, not placing constraints on who is online at all. Also, if both
>> siblings are offline, then onlining will re-load ucode anyway, no?
>
> We need one thread in a core online,  because a MCE can happen and we don't
> want those running something stale.

Nonsense. This is a constraint at boot time. But afterwards it does not
matter at all. That's what Peter is talking about.