[PATCH v2 10/12] x86,nospec: Simplify {JMP,CALL}_NOSPEC (part 2)

[Peter Zijlstra <peterz@infradead.org>]

Counterpart to 09d09531a51a ("x86,nospec: Simplify
{JMP,CALL}_NOSPEC"), x86_64 will rewrite all this anyway, see
apply_retpoline.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/nospec-branch.h |   29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -429,31 +429,24 @@ static inline void call_depth_return_thu
 
 #ifdef CONFIG_X86_64
 
+#define __CS_PREFIX						\
+	".irp rs,r8,r9,r10,r11,r12,r13,r14,r15\n"		\
+	".ifc %V[thunk_target],\\rs\n"				\
+	".byte 0x2e\n"						\
+	".endif\n"						\
+	".endr\n"
+
 /*
  * Inline asm uses the %V modifier which is only in newer GCC
  * which is ensured when CONFIG_MITIGATION_RETPOLINE is defined.
  */
 # define CALL_NOSPEC						\
-	ALTERNATIVE_2(						\
-	ANNOTATE_RETPOLINE_SAFE					\
-	"call *%[thunk_target]\n",				\
-	"call __x86_indirect_thunk_%V[thunk_target]\n",		\
-	X86_FEATURE_RETPOLINE,					\
-	"lfence;\n"						\
-	ANNOTATE_RETPOLINE_SAFE					\
-	"call *%[thunk_target]\n",				\
-	X86_FEATURE_RETPOLINE_LFENCE)
+	__CS_PREFIX						\
+	"call __x86_indirect_thunk_%V[thunk_target]\n"
 
 # define JMP_NOSPEC						\
-	ALTERNATIVE_2(						\
-	ANNOTATE_RETPOLINE_SAFE					\
-	"jmp *%[thunk_target]\n",				\
-	"jmp __x86_indirect_thunk_%V[thunk_target]\n",		\
-	X86_FEATURE_RETPOLINE,					\
-	"lfence;\n"						\
-	ANNOTATE_RETPOLINE_SAFE					\
-	"jmp *%[thunk_target]\n",				\
-	X86_FEATURE_RETPOLINE_LFENCE)
+	__CS_PREFIX						\
+	"jmp __x86_indirect_thunk_%V[thunk_target]\n"
 
 # define THUNK_TARGET(addr) [thunk_target] "r" (addr)