From 362e4a9b0a930180c571f2aff9d035649582a3c3 Mon Sep 17 00:00:00 2001
From: Michal Suchanek <msuchanek@suse.de>
Date: Tue, 24 Apr 2018 14:15:54 +1000
Subject: [PATCH] powerpc/64s: Add barrier_nospec

References: bsc#1068032, bsc#1080157
Patch-mainline: v4.18-rc1
Git-commit: a6b3964ad71a61bb7c61d80a60bea7d42187b2eb

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 <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 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 25d42bd3f114..4494e3586f3f 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -81,6 +81,21 @@ do {									\
  */
 #define smp_mb__before_spinlock()   smp_mb()
 
+#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 <asm-generic/barrier.h>
 
 #endif /* _ASM_POWERPC_BARRIER_H */
-- 
2.13.6