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

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Date:	Fri, 19 Sep 2014 14:22:18 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	"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, Borislav Petkov wrote:
> On Fri, Sep 19, 2014 at 10:51:08AM -0300, Henrique de Moraes Holschuh wrote:
> > But I will not trigger a microcode update when the intel-microcode package
> > gets updated/installed anymore.  The user will be warned of the need for
> > either a reboot or a manually triggered microcode update.
> 
> That's also wrong - you need to warn only on the affected machines.

I could enhance iucode_tool so that it can tell you when there are pending
updates.  But it is a layering violation I don't like much, and it is a lot
less future-proof than the stuff iucode-tool already does.  I will think
about it... but I'm inclined to just tell the user that "microcode updates,
if any, will be applied the next time this system reboots".

As for immediately updating the microcode on all processors other than Intel
Haswell: this time, Felix Geyer found the issue early enough to save both
Ubuntu and Debian users from harm, and I brought it to attention here as
soon as I had a good idea of what was happening.

But this was a close call as far as I'm concerned.  Next time, we might not
be so lucky.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh
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