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Date: Tue, 20 Feb 2018 01:03:19 +0000
From: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
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Subject: Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future
 CPUs
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On Mon, 19 Feb 2018 16:43:50 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, Feb 19, 2018 at 4:13 PM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote:
> >
> > In theory there's nothing stopping a guest getting a 'you are about to
> > gain/lose IBRS' message or having a new 'CPU' hotplugged and the old one
> > removed.  
> 
> I'm not convinced we handle the case of hotplug CPU's with different
> CPU models correctly.

We don't. And even if we did the user space doesn't. It would be a
painful task to resolve.

Alan