linux-kernel - Re: [PATCH] x86/microcode/AMD: Attempt applying on every logical thread

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Date:   Wed, 17 Aug 2022 23:56:02 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ashok Raj <ashok.raj@...el.com>
Cc:     Ashok Raj <ashok_raj@...ux.intel.com>, X86 ML <x86@...nel.org>,
        Andrew Cooper <amc96@...f.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Ștefan Talpalaru <stefantalpalaru@...oo.com>
Subject: Re: [PATCH] x86/microcode/AMD: Attempt applying on every logical
 thread

On Wed, Aug 17, 2022 at 08:58:07PM +0000, Ashok Raj wrote:
> For this specific patch in question, its not for testing though.. Its
> required for functional purposes?

>From its commit message:

"However, there are microcode patches which do per-thread modification,
see Link tag below.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216211"

TL;DR - the application needs to happen on *every* logical CPU.

> In effect you can test applying the same microcode over and over again
> without having any special patches. 

Right now, you cannot downgrade on Zen but apparently applying the same
patch over and over again works.

The patch cache still has a version check and that prevents it but
that's ugly.

I need to test how it behaves on older families first and then think
about how to do this right. Maybe use cpuinfo_x86.microcode to record
what has been applied until now...

-- 
Regards/Gruss,
    Boris.

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