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From:   Michal Suchanek <msuchanek@suse.de>
To:     linuxppc-dev@lists.ozlabs.org
Cc:     Kate Stewart <kstewart@linuxfoundation.org>,
        Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
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        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
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        Oliver O'Halloran <oohall@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Tobin C. Harding" <me@tobin.cc>,
        Michal Suchanek <msuchanek@suse.de>
Subject: [PATCH RFC rebase 1/9] powerpc: Add barrier_nospec
Date:   Thu, 15 Mar 2018 20:15:50 +0100
Message-Id: <8cb7d41beef9bdd351120d0512f73ac3bfada168.1521141122.git.msuchanek@suse.de>
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When the firmware supports it an otherwise useless combination of ORI
instruction arguments is interpreted as speculation barrier. Implement
barrier_nospec using this instruction.

Based on the out-of-tree gmb() implementation.

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/include/asm/barrier.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index 10daa1d56e0a..8e47b3abe405 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -75,6 +75,15 @@ do {									\
 	___p1;								\
 })
 
+/* TODO: add patching so this can be disabled */
+/* Prevent speculative execution past this barrier. */
+#define barrier_nospec_asm ori 31,31,0
+#ifdef __ASSEMBLY__
+#define barrier_nospec barrier_nospec_asm
+#else
+#define barrier_nospec() __asm__ __volatile__ (stringify_in_c(barrier_nospec_asm) : : :)
+#endif
+
 #include <asm-generic/barrier.h>
 
 #endif /* _ASM_POWERPC_BARRIER_H */
-- 
2.13.6