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

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Message-ID: <20140919075415.5149d5f2@as>
Date:	Fri, 19 Sep 2014 07:54:14 -0500
From:	Chuck Ebbert <cebbert.lkml@...il.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	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, 19 Sep 2014 13:29:53 +0200
Borislav Petkov <bp@...en8.de> wrote:

> On Fri, Sep 19, 2014 at 08:00:15AM -0300, Henrique de Moraes Holschuh wrote:
> > We're also killing microcode update support outside of the initramfs in
> > Debian.  It has become obvious that anything other than the early initramfs
> > method of microcode updates should be considered a developer thing.
> 
> That's simply not true: long-running systems which you can't reboot for
> whatever reason will need the late microcode update.
> 

Assuming we can identify all the affected models and steppings, maybe
something like this would work:

1) Refuse to finish booting if a microcode update that disables TSX
isn't applied before userspace starts running on those CPUs.

and/or

2) Don't allow a late update if TSX is still enabled on those
processors.

(1) could be overridden by a command line option for people who want to
develop TSX code.
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