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

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Date:   Wed, 17 Aug 2022 20:13:15 +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 03:29:04PM +0000, Ashok Raj wrote:
> What I meant was the patch removed any and all revid checks *completely*
> Instead of even limiting to == checks.

I just tried downgrading the microcode on an AMD box. The hardware
wouldn't accept the MSR write with the lower patch ID and the higher
patch ID remained.

I'll find out whether this is universally the case on AMD.

> So forget the hardware testing part. This is a complex flow for
> late-load and how can we get more people to test it today in the
> community?

> Do we have a more scalable way to support it today?

You're not reading my mails. Lemme repeat: microcode loading is a
dangerous business, especially the late thing. I'm certainly not going
to expose that to people if there's no merit. The only merit for loading
the same revision is for testing purposes.

If you're about to test stuff, you can just as well patch the microcode
loader to do what you want it to, like I just did.

-- 
Regards/Gruss,
    Boris.

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