linux-kernel - Re: [PATCH] x86/microcode: Add an option to reload microcode even if revision is unchanged

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Message-ID: <20190906171720.GM19008@zn.tnic>
Date:   Fri, 6 Sep 2019 19:17:20 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Johannes Erdfelt <johannes@...felt.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Mihai Carabas <mihai.carabas@...cle.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jon Grimm <Jon.Grimm@....com>, kanth.ghatraju@...cle.com,
        konrad.wilk@...cle.com, patrick.colp@...cle.com,
        Tom Lendacky <thomas.lendacky@....com>,
        x86-ml <x86@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/microcode: Add an option to reload microcode even if
 revision is unchanged

On Fri, Sep 06, 2019 at 09:52:07AM -0700, Johannes Erdfelt wrote:
> That doesn't mean that late loading isn't still useful.

If it weren't useful, it would've been gone a long time ago. No one is
arguing whether it is useful or not.

> Just as I can't know for sure that every future microcode update will be
> safely late loadable, you can't know for sure that every future microcode
> update won't be safely late loadable.

Well, you know what can happen so good luck, I guess.

> We do use other techniques as well particularly when it's not time
> sensitive.

So you reboot or not? Do you do reboot-similar techniques where you can
potentially do early microcode loading too?

> It very much makes it right because it's still a tool that can be used
> safely in the right cases. Just because it can't be used 100% of the time
> (even if it is close to that in practice) doesn't make it magically unsafe
> either.

As I said, good luck with that. It's not like you haven't been warned
about what can happen.

-- 
Regards/Gruss,
    Boris.

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