On Fri, 2018-01-26 at 18:44 +0000, Van De Ven, Arjan wrote:
> your question was specific to RSB not BTB. But please show the empirical evidence for RSB ?

We were hypothesising, which should have been clear from:

On Fri, 2018-01-26 at 09:11 +0000, David Woodhouse wrote:
> Likewise if the RSB only stores the low 31 bits of the target, SMEP
> isn't much help there either.
> 
> Do we need to look again at the fact that we've disabled the RSB-
> stuffing for SMEP?

... and later... 

On Fri, 2018-01-26 at 17:31 +0000, David Woodhouse wrote:
> Note, we've switched from talking about BTB to RSB here, so this is a
> valid concern if the *RSB* only has the low bits of the target.

I'm glad to hear that it *isn't* a valid concern for the RSB and the
code in Linus' tree is correct.

Thank you for clearing that up.