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Date:   Sat, 8 Sep 2018 08:36:03 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Andy Lutomirski <luto@kernel.org>
cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        the arch/x86 maintainers <x86@kernel.org>,
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        Joerg Roedel <joro@8bytes.org>, Jiri Olsa <jolsa@redhat.com>,
        Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH v2 3/3] x86/pti/64: Remove the SYSCALL64 entry
 trampoline
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On Fri, 7 Sep 2018, Andy Lutomirski wrote:
> On Fri, Sep 7, 2018 at 5:04 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> > Virtual mapping tricks may be cool, but in the end, not having to use
> > them is better still, I think.
> >
> 
> If (and this is a *big* if) all the percpu data is within 2GB of the
> entry text, then we could avoid this extra TLB reference by accessing
> it directly instead of using an alias.
> 
> I suppose the summary is that the retpoline-free trampoline variant is
> even more complicated than the code I'm removing in this series, and
> that it would be at best a teeny tiny win.  Once all the Spectre dust
> settles and we get fixed CPUs, we could consider re-optimizing this.

That's going to be after my retirement ...