Re: [patch RFC 5/5] x86/speculation: Add basic speculation control code

[Peter Zijlstra]

On Wed, Jan 10, 2018 at 09:27:59AM +0000, David Woodhouse wrote:
> > The only question I have is if retpoline works at all on SKL (with ucode
> > update); BDW needs the ucode update for retpoline to work because of the
> > RSB fallback.
> 
> As I understand it, Skylake is never getting the IBRS_ATT (all the
> time) feature. That is for future CPUs only.

Ah, so then I got confused by your earlier email. So retpoline will work
on SKL, but it will, like BDW need the ucode update?

> I don't know why you're calling that 'IBRS=2'; are you getting confused
> by Andrea's distro horridness?

Yes, continuation of the nomenclature of that earlier thread.

Still, point remains, do we ever need that MSR fiddling dynamic IBRS
stuff now that we have retpolines? I would prefer to not have it if
there is no compelling reason for it.