linux-kernel - [PATCH 3.16 060/410] x86/speculation: Move firmware_restrict_branch_speculation

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Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, rkrcmar@...hat.com,
        dave.hansen@...el.com, arjan.van.de.ven@...el.com,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Thomas Gleixner" <tglx@...utronix.de>, kvm@...r.kernel.org,
        karahmed@...zon.de, "Ingo Molnar" <mingo@...nel.org>,
        pbonzini@...hat.com, jmattson@...gle.com,
        "Peter Zijlstra" <peterz@...radead.org>, bp@...en8.de,
        "David Woodhouse" <dwmw@...zon.co.uk>
Subject: [PATCH 3.16 060/410] x86/speculation: Move firmware_restrict_branch_speculation_*()
 from C  to CPP

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ingo Molnar <mingo@...nel.org>

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@...zon.co.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: arjan.van.de.ven@...el.com
Cc: bp@...en8.de
Cc: dave.hansen@...el.com
Cc: jmattson@...gle.com
Cc: karahmed@...zon.de
Cc: kvm@...r.kernel.org
Cc: pbonzini@...hat.com
Cc: rkrcmar@...hat.com
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/include/asm/nospec-branch.h | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -213,20 +213,22 @@ static inline void indirect_branch_predi
 /*
  * 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__ */
 #endif /* _ASM_X86_NOSPEC_BRANCH_H_ */