x86/speculation: Move firmware_restrict_branch_speculation_*() from C to CPP

commit d72f4e29e6d84b7ec02ae93088aa459ac70e733b upstream.

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@amazon.co.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: arjan.van.de.ven@intel.com
Cc: bp@alien8.de
Cc: dave.hansen@intel.com
Cc: jmattson@google.com
Cc: karahmed@amazon.de
Cc: kvm@vger.kernel.org
Cc: pbonzini@redhat.com
Cc: rkrcmar@redhat.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 29e8f30..d0dabea 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -257,20 +257,22 @@ 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__ */