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

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Date:   Tue, 31 Jan 2023 21:40:40 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
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

On Tue, Jan 31, 2023 at 05:34:14PM +0000, Luck, Tony wrote:
> But those get out of step when applying ucode on one logical CPU does
> an update to other(s) (in this case the HT sibling for the same core).

They shouldn't.

I presume you're talking about late update. If so and if it finds a
patch in the cache, it'll do this:

apply_microcode_intel:

        /*
         * Save us the MSR write below - which is a particular expensive
         * operation - when the other hyperthread has updated the microcode
         * already.
         */
        rev = intel_get_microcode_revision();
        if (rev >= mc->hdr.rev) {
                ret = UCODE_OK;
                goto out;
        }

and at the out: label it'll update the revision.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette