Re: [v3 03/12] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions

[Andy Lutomirski]

On Tue, Oct 23, 2018 at 11:43 AM Chang S. Bae <chang.seok.bae@xxxxxxxxx> wrote:
>
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>
> Add C intrinsics and assembler macros for the new FSBASE and GSBASE
> instructions.
>
> Very straight forward. Used in followon patches.
>
> [ luto: Rename the variables from FS and GS to FSBASE and GSBASE and
>   make <asm/fsgsbase.h> safe to include on 32-bit kernels. ]
>
> v2: Use __always_inline
>
> [ chang: Revise the changelog. Place them in <asm/fsgsbase.h>. Replace
>   the macros with GAS-compatible ones. ]
>
> If GCC supports it, we can add -mfsgsbase to CFLAGS and use the builtins
> here for extra performance.

Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx> # C parts only

With the caveat that I'm not convinced that the memory clobbers are
needed.  The __force_order trick in special_insns.h would probably be
more appropriate.

I don't feel qualified to review the asm part without some research.
Whereas hpa or Boris could probably review it with their eyes closed.