[PATCH 14/24] x86/speculation: Move firmware_restrict_branch_speculation_*() from C to CPP

[Youquan Song <youquan.song@xxxxxxxxx>]

From: Ingo Molnar <mingo@xxxxxxxxxx>

(cherry picked from commit d72f4e29e6d84b7ec02ae93088aa459ac70e733b)

firmware_restrict_branch_speculation_*() recently started using
preempt_enable()/disable(), but those are relatively high level
primitives and cause build failures on some 32-bit builds.

Since we want to keep <asm/nospec-branch.h> low level, convert
them to macros to avoid header hell...

Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: arjan.van.de.ven@xxxxxxxxx
Cc: bp@xxxxxxxxx
Cc: dave.hansen@xxxxxxxxx
Cc: jmattson@xxxxxxxxxx
Cc: karahmed@xxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Cc: pbonzini@xxxxxxxxxx
Cc: rkrcmar@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Youquan Song <youquan.song@xxxxxxxxxxxxxxx> [v4.4 backport]
---
 arch/x86/include/asm/nospec-branch.h | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 27582aa..4675f65 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -214,20 +214,22 @@ static inline void indirect_branch_prediction_barrier(void)
 /*
  * With retpoline, we must use IBRS to restrict branch prediction
  * before calling into firmware.
+ *
+ * (Implemented as CPP macros due to header hell.)
  */
-static inline void firmware_restrict_branch_speculation_start(void)
-{
-	preempt_disable();
-	alternative_msr_write(MSR_IA32_SPEC_CTRL, SPEC_CTRL_IBRS,
-			      X86_FEATURE_USE_IBRS_FW);
-}
+#define firmware_restrict_branch_speculation_start()			\
+do {									\
+	preempt_disable();						\
+	alternative_msr_write(MSR_IA32_SPEC_CTRL, SPEC_CTRL_IBRS,	\
+			      X86_FEATURE_USE_IBRS_FW);			\
+} while (0)
 
-static inline void firmware_restrict_branch_speculation_end(void)
-{
-	alternative_msr_write(MSR_IA32_SPEC_CTRL, 0,
-			      X86_FEATURE_USE_IBRS_FW);
-	preempt_enable();
-}
+#define firmware_restrict_branch_speculation_end()			\
+do {									\
+	alternative_msr_write(MSR_IA32_SPEC_CTRL, 0,			\
+			      X86_FEATURE_USE_IBRS_FW);			\
+	preempt_enable();						\
+} while (0)
 
 #endif /* __ASSEMBLY__ */
 
-- 
1.8.3.1