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Date:	Fri, 19 Sep 2014 10:03:22 +0200
From:	Borislav Petkov <>
To:	Andy Lutomirski <>
Cc:	"H. Peter Anvin" <>,
	"" <>,
	Chuck Ebbert <>,
	Henrique de Moraes Holschuh <>
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.

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