From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751603AbeDXEQK (ORCPT ); Tue, 24 Apr 2018 00:16:10 -0400 Received: from ozlabs.org ([203.11.71.1]:48415 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750962AbeDXEQI (ORCPT ); Tue, 24 Apr 2018 00:16:08 -0400 From: Michael Ellerman To: linuxppc-dev@ozlabs.org Cc: npiggin@gmail.com, msuchanek@suse.de, linux-kernel@vger.kernel.org Subject: [PATCH 1/6] powerpc/64s: Add barrier_nospec Date: Tue, 24 Apr 2018 14:15:54 +1000 Message-Id: <20180424041559.32410-1-mpe@ellerman.id.au> X-Mailer: git-send-email 2.14.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Michal Suchanek A no-op form of ori (or immediate of 0 into r31 and the result stored in r31) has been re-tasked as a speculation barrier. The instruction only acts as a barrier on newer machines with appropriate firmware support. On older CPUs it remains a harmless no-op. Implement barrier_nospec using this instruction. mpe: The semantics of the instruction are believed to be that it prevents execution of subsequent instructions until preceding branches have been fully resolved and are no longer executing speculatively. There is no further documentation available at this time. Signed-off-by: Michal Suchanek Signed-off-by: Michael Ellerman --- mpe: Make it Book3S64 only, update comment & change log, add a memory clobber to the asm. --- arch/powerpc/include/asm/barrier.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h index c7c63959ba91..e582d2c88092 100644 --- a/arch/powerpc/include/asm/barrier.h +++ b/arch/powerpc/include/asm/barrier.h @@ -76,6 +76,21 @@ do { \ ___p1; \ }) +#ifdef CONFIG_PPC_BOOK3S_64 +/* + * Prevent execution of subsequent instructions until preceding branches have + * been fully resolved and are no longer executing speculatively. + */ +#define barrier_nospec_asm ori 31,31,0 + +// This also acts as a compiler barrier due to the memory clobber. +#define barrier_nospec() asm (stringify_in_c(barrier_nospec_asm) ::: "memory") + +#else /* !CONFIG_PPC_BOOK3S_64 */ +#define barrier_nospec_asm +#define barrier_nospec() +#endif + #include #endif /* _ASM_POWERPC_BARRIER_H */ -- 2.14.1