Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs

[Alan Cox]

On Mon, 19 Feb 2018 16:43:50 -0800
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Mon, Feb 19, 2018 at 4:13 PM, Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx> 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