powerpc/64s: Add barrier_nospec

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 <[email protected]> Signed-off-by: Michael Ellerman <[email protected]>
yishaih · Jun 3, 2018 · a6b3964 · a6b3964
1 parent 7af76c5
commit a6b3964
Showing 1 changed file with 15 additions and 0 deletions.
diff --git 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 <asm-generic/barrier.h>
 
 #endif /* _ASM_POWERPC_BARRIER_H */