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Date: Wed, 10 Jan 2018 13:27:55 +0100
From: Andrea Arcangeli <aarcange@redhat.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@intel.com>,
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        Greg KH <gregkh@linuxfoundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>
Subject: Re: [patch RFC 5/5] x86/speculation: Add basic speculation control
 code
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On Wed, Jan 10, 2018 at 01:20:45PM +0100, Andrea Arcangeli wrote:
> On Wed, Jan 10, 2018 at 12:12:53PM +0000, David Woodhouse wrote:
> > IBRS is like a barrier. You must write it between the 'problematic'
> > loading of the branch targets, and the kernel code which might be
> > affected.
> > 
> > You cannot, on current hardware, merely set it once and forget about
> > it. That is not sufficient.
> 
> I think you've got it all wrong...

On a side note, I hope once you get it right, the debugfs tunable will
suddenly look less horrid.