linux-kernel - [tip: x86/cpu] x86/speculation: Simplify and make CALL

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Message-ID: <174108398503.14745.3531917844748876019.tip-bot2@tip-bot2>
Date: Tue, 04 Mar 2025 10:26:25 -0000
From: "tip-bot2 for Pawan Gupta" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Ingo Molnar <mingo@...nel.org>, Andrew Cooper <andrew.cooper3@...rix.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: x86/cpu] x86/speculation: Simplify and make CALL_NOSPEC consistent

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     cfceff8526a426948b53445c02bcb98453c7330d
Gitweb:        https://git.kernel.org/tip/cfceff8526a426948b53445c02bcb98453c7330d
Author:        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
AuthorDate:    Fri, 28 Feb 2025 18:35:43 -08:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 04 Mar 2025 11:14:35 +01:00

x86/speculation: Simplify and make CALL_NOSPEC consistent

CALL_NOSPEC macro is used to generate Spectre-v2 mitigation friendly
indirect branches. At compile time the macro defaults to indirect branch,
and at runtime those can be patched to thunk based mitigations.

This approach is opposite of what is done for the rest of the kernel, where
the compile time default is to replace indirect calls with retpoline thunk
calls.

Make CALL_NOSPEC consistent with the rest of the kernel, default to
retpoline thunk at compile time when CONFIG_MITIGATION_RETPOLINE is
enabled.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Andrew Cooper <andrew.cooper3@...rix.com
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: https://lore.kernel.org/r/20250228-call-nospec-v3-1-96599fed0f33@linux.intel.com
---
 arch/x86/include/asm/nospec-branch.h | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 7e8bf78..1e6b915 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -424,16 +424,11 @@ static inline void call_depth_return_thunk(void) {}
  * 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)
+#ifdef CONFIG_MITIGATION_RETPOLINE
+#define CALL_NOSPEC	"call __x86_indirect_thunk_%V[thunk_target]\n"
+#else
+#define CALL_NOSPEC	"call *%[thunk_target]\n"
+#endif
 
 # define THUNK_TARGET(addr) [thunk_target] "r" (addr)