linux-kernel - RE: [Patch v3 Part2 3/9] x86/microcode/intel: Fix collect_cpu

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Message-ID: <SJ1PR11MB60832B131FF4FA87E21C62CFFCD19@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Wed, 1 Feb 2023 16:15:47 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "Raj, Ashok" <ashok.raj@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Schofield, Alison" <alison.schofield@...el.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Stefan Talpalaru" <stefantalpalaru@...oo.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Jonathan Corbet <corbet@....net>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Peter Zilstra <peterz@...radead.org>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Ostrovsky, Boris" <boris.ostrovsky@...cle.com>,
        Martin Pohlack <mpohlack@...zon.de>
Subject: RE: [Patch v3 Part2 3/9] x86/microcode/intel: Fix collect_cpu_info()
 to reflect current microcode

> So first of all, I'm wondering whether the scenario you're chasing is
> something completely hypothetical or you're actually thinking of
> something concrete which has actually happened or there's high potential
> for it.

Rare, but very real. For one of the speculative side channel microcode
updates there were some reports from large data centers that the kernel
choked on a WRMSR(IA32_SPEC_CTRL)

> In that case, that late patching sync algorithm would need to be made
> more robust to handle cases like that.
"
Yup. when you get through the cleanups and the "minrev" update Ashok
has a handful of final[1] patches that add robustness.

-Tony

[1] Yes, there is an end in sight to all these microcode changes.