On Sat, 2018-01-13 at 13:08 +0100, Peter Zijlstra wrote:
> 
>         ALTERNATIVE "orq $(PTI_SWITCH_PGTABLE_MASK), \scratch_reg",
>                     "orq $(PTI_SWITCH_MASK), \scratch_reg", X86_FEATURE_PCID
> 
> Is not wanting to compile though; probably that whole alternative vs
> macro thing again :/

Welcome to my world. Try

 ALTERNATIVE __stringify(orq $(PTI_SWITCH_PGTABLE_MASK), \scratch_reg), \
             __stringify(orq $(PTI_SWITCH_MASK), \scratch_reg), \
             X86_FEATURE_PCID