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

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Message-ID: <20140925164121.GC10814@khazad-dum.debian.net>
Date:	Thu, 25 Sep 2014 13:41:21 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Borislav Petkov <bp@...en8.de>
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 Thu, 25 Sep 2014, Borislav Petkov wrote:
> On Thu, Sep 25, 2014 at 12:30:06PM -0300, Henrique de Moraes Holschuh wrote:
> > Userspace can install the microcode only inside the initramfs, if it wants
> > to avoid it being loaded later.  It is not even too difficult to do so.
> 
> Hmm, so in thinking about this more, what we need to do on all kernels
> should be something along those lines (if I'm not missing something,
> that is):
> 
> 
> 	if (early microcode loading support) {
> 		install microcode into initramfs;
> 	}
> 
> 	install microcode into /lib/firmware/...;
> 	tell the user to reboot;
> 
> On the next reboot, everything gets loaded automatically.
> 
> Of course, user needs to make sure that the microcode loader module gets
> loaded during boot. If its built-in, we're fine.

We still need to update x86_capability after a microcode update for the
above to really work in the "install microcode into initramfs" case.

-- 
  "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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