linux-kernel - [PATCH -tip v2] x86/idle: Work around LLVM assembler bug with MONITOR and MWAIT insn

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Message-ID: <20250403091737.344149-1-ubizjak@gmail.com>
Date: Thu,  3 Apr 2025 11:17:19 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: x86@...nel.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	kernel test robot <lkp@...el.com>
Subject: [PATCH -tip v2] x86/idle: Work around LLVM assembler bug with MONITOR and MWAIT insn

LLVM assembler is not able to assemble correct forms of MONITOR
and MWAIT instructions with explicit operands:

  error: invalid operand for instruction
          monitor %rax,%ecx,%edx
                       ^~~~

Use instruction mnemonics with implicit operands to
work around this issue.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Fixes: cd3b85b27542 ("x86/idle: Use MONITOR and MWAIT mnemonics in <asm/mwait.h>")
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202504030802.2lEVBSpN-lkp@intel.com/
---
v2: Use instruction mnemonics with implicit operands.
---
 arch/x86/include/asm/mwait.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 5141d2acc0ef..8f2cfc9cc3d8 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -27,7 +27,7 @@
 
 static __always_inline void __monitor(const void *eax, u32 ecx, u32 edx)
 {
-	asm volatile("monitor %0, %1, %2" :: "a" (eax), "c" (ecx), "d" (edx));
+	asm volatile("monitor" :: "a" (eax), "c" (ecx), "d" (edx));
 }
 
 static __always_inline void __monitorx(const void *eax, u32 ecx, u32 edx)
@@ -41,7 +41,7 @@ static __always_inline void __mwait(u32 eax, u32 ecx)
 {
 	mds_idle_clear_cpu_buffers();
 
-	asm volatile("mwait %0, %1" :: "a" (eax), "c" (ecx));
+	asm volatile("mwait" :: "a" (eax), "c" (ecx));
 }
 
 /*
@@ -92,7 +92,7 @@ static __always_inline void __sti_mwait(u32 eax, u32 ecx)
 {
 	mds_idle_clear_cpu_buffers();
 
-	asm volatile("sti; mwait %0, %1" :: "a" (eax), "c" (ecx));
+	asm volatile("sti; mwait" :: "a" (eax), "c" (ecx));
 }
 
 /*
-- 
2.49.0