On Fri, 2018-01-05 at 16:11 -0500, Brian Gerst wrote:
> 
> Another way to do it is with two consecutive alternatives:
> 
> ALTERNATIVE(NOP, K8: lfence)
> ALTERNATIVE(jmp indirect, RETPOLINE: jmp thunk)
> 
> This also avoids the issue with the relocation of the jmp target when
> the replacement is more than one instruction.

You'd still want a RETPOLINE_AMD flag to enable that lfence; it's not
just K8.