linux-kernel - [PATCH -tip] x86/asm: Replace "REP; NOP" with PAUSE mnemonic

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Message-ID: <20250414145033.10511-1-ubizjak@gmail.com>
Date: Mon, 14 Apr 2025 16:50:17 +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>
Subject: [PATCH -tip] x86/asm: Replace "REP; NOP" with PAUSE mnemonic

Current minimum required version of binutils is 2.25,
which supports PAUSE instruction mnemonic.

Replace "REP; NOP" with this proper mnemonic.

No functional change intended.

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>
---
 arch/x86/boot/boot.h                  | 2 +-
 arch/x86/include/asm/vdso/processor.h | 2 +-
 arch/x86/kernel/relocate_kernel_64.S  | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index f3771a6373c7..60580836daf7 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -34,7 +34,7 @@
 extern struct setup_header hdr;
 extern struct boot_params boot_params;
 
-#define cpu_relax()	asm volatile("rep; nop")
+#define cpu_relax()	asm volatile("pause")
 
 static inline void io_delay(void)
 {
diff --git a/arch/x86/include/asm/vdso/processor.h b/arch/x86/include/asm/vdso/processor.h
index c9b2ba7a9ec4..02b8340c6546 100644
--- a/arch/x86/include/asm/vdso/processor.h
+++ b/arch/x86/include/asm/vdso/processor.h
@@ -10,7 +10,7 @@
 /* REP NOP (PAUSE) is a good thing to insert into busy-wait loops. */
 static __always_inline void rep_nop(void)
 {
-	asm volatile("rep; nop" ::: "memory");
+	asm volatile("pause" ::: "memory");
 }
 
 static __always_inline void cpu_relax(void)
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 1d6355227bf6..ea604f4d0b52 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -405,7 +405,7 @@ SYM_CODE_START_LOCAL_NOALIGN(pr_char_8250)
 	inb	%dx, %al
 	testb	$XMTRDY, %al
 	jnz	.Lready
-	rep nop
+	pause
 	jmp .Lxmtrdy_loop
 
 .Lready:
@@ -426,7 +426,7 @@ SYM_CODE_START_LOCAL_NOALIGN(pr_char_8250_mmio32)
 	movb	(LSR*4)(%rdx), %ah
 	testb	$XMTRDY, %ah
 	jnz	.Lready_mmio
-	rep nop
+	pause
 	jmp .Lxmtrdy_loop_mmio
 
 .Lready_mmio:
-- 
2.42.0