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

Commit-ID:     defea9e60d3f440ca8da070a478f668fec0ba659
Gitweb:        https://git.kernel.org/tip/defea9e60d3f440ca8da070a478f668fec0ba659
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Thu, 03 Apr 2025 14:50:45 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 03 Apr 2025 15:27:50 +02:00

x86/idle: Use MONITOR and MWAIT mnemonics in <asm/mwait.h>

Current minimum required version of binutils is 2.25,
which supports MONITOR and MWAIT instruction mnemonics.

Replace the byte-wise specification of MONITOR and
MWAIT with these proper mnemonics.

No functional change intended.

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

  error: invalid operand for instruction
          monitor %rax,%ecx,%edx
                       ^~~~
  # https://lore.kernel.org/oe-kbuild-all/202504030802.2lEVBSpN-lkp@intel.com/

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

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250403125111.429805-1-ubizjak@gmail.com
---
 arch/x86/include/asm/mwait.h | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 6a2ec20..26b68ee 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -27,9 +27,9 @@
 
 static __always_inline void __monitor(const void *eax, u32 ecx, u32 edx)
 {
-	/* "monitor %eax, %ecx, %edx;" */
-	asm volatile(".byte 0x0f, 0x01, 0xc8;"
-		     :: "a" (eax), "c" (ecx), "d"(edx));
+	/* Use the instruction mnemonic with implicit operands, as the LLVM
+	   assembler fails to assemble the mnemonic with explicit operands. */
+	asm volatile("monitor" :: "a" (eax), "c" (ecx), "d" (edx));
 }
 
 static __always_inline void __monitorx(const void *eax, u32 ecx, u32 edx)
@@ -43,9 +43,9 @@ static __always_inline void __mwait(u32 eax, u32 ecx)
 {
 	mds_idle_clear_cpu_buffers();
 
-	/* "mwait %eax, %ecx;" */
-	asm volatile(".byte 0x0f, 0x01, 0xc9;"
-		     :: "a" (eax), "c" (ecx));
+	/* Use the instruction mnemonic with implicit operands, as the LLVM
+	   assembler fails to assemble the mnemonic with explicit operands. */
+	asm volatile("mwait" :: "a" (eax), "c" (ecx));
 }
 
 /*
@@ -95,9 +95,8 @@ static __always_inline void __mwaitx(u32 eax, u32 ebx, u32 ecx)
 static __always_inline void __sti_mwait(u32 eax, u32 ecx)
 {
 	mds_idle_clear_cpu_buffers();
-	/* "mwait %eax, %ecx;" */
-	asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
-		     :: "a" (eax), "c" (ecx));
+
+	asm volatile("sti; mwait" :: "a" (eax), "c" (ecx));
 }
 
 /*