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

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Date:	Fri, 19 Sep 2014 10:03:22 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>
Subject: Re: x86, microcode: BUG: microcode update that changes x86_capability

On Thu, Sep 18, 2014 at 06:00:12PM -0700, Andy Lutomirski wrote:
> Yes, but how?  I assume that BIOS isn't switching between two
> different ucode blobs, and I don't know about any wrcpuid instruction.
> So there must be *some* way, at least on new ucode (and maybe on old
> ucode) to change that bit.

I'd venture a guess that WRMSR to some reg should give you that, if they
expose it.

-- 
Regards/Gruss,
    Boris.
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