linux-kernel - Re: x86, microcode: BUG: microcode update that changes x86

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Message-ID: <20140923200054.GB16467@pd.tnic>
Date:	Tue, 23 Sep 2014 22:00:54 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Chuck Ebbert <cebbert.lkml@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: x86, microcode: BUG: microcode update that changes x86_capability

On Fri, Sep 19, 2014 at 01:42:17PM -0300, Henrique de Moraes Holschuh wrote:
> 1. offline a "guinea pig" group of "cpus", i.e. an entire "microcode update
> unit" that doesn't include the BSP.  This is going to be a pain, as what
> composes a "microcode update unit" is not set in stone, and could change in
> a future microarch.

I'm pretty sure it is very dangerous to run with different microcode
revisions on different cores. Your plan won't fly and I have hard time
understanding why one would do such thing even if it did work.

If we're going to have to hide stuff which software might be using, I
don't see a way around rebooting.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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