Re: [PATCH v2 3/3] x86/pti/64: Remove the SYSCALL64 entry trampoline

Thomas Gleixner
2018-09-08T06:36:12Z

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 ...