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

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Date:	Fri, 19 Sep 2014 09:14:50 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Chuck Ebbert <cebbert.lkml@...il.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	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, Sep 19, 2014 at 8:54 AM, Chuck Ebbert <cebbert.lkml@...il.com> wrote:
> 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.

How would you accomplish that when applying a microcode update
requires userspace?  Or did you mean "before we transition out of the
initramfs"?

josh
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