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

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Message-ID: <174496598484.31282.5671192677885545892.tip-bot2@tip-bot2>
Date: Fri, 18 Apr 2025 08:46:24 -0000
From: "tip-bot2 for Uros Bizjak" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Nikolay Borisov <nik.borisov@...e.com>, Uros Bizjak <ubizjak@...il.com>,
 Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/asm] x86/asm: Replace "REP; NOP" with PAUSE mnemonic

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

Commit-ID:     d109ff4f0bc32de354247a6e8ede3ffc8ef14cd0
Gitweb:        https://git.kernel.org/tip/d109ff4f0bc32de354247a6e8ede3ffc8ef14cd0
Author:        Uros Bizjak <ubizjak@...il.com>
AuthorDate:    Fri, 18 Apr 2025 10:07:44 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 18 Apr 2025 10:19:25 +02:00

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.

Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: H. Peter Anvin <hpa@...or.com>
Link: https://lore.kernel.org/r/20250418080805.83679-2-ubizjak@gmail.com
---
 arch/x86/boot/boot.h                  | 2 +-
 arch/x86/include/asm/vdso/processor.h | 4 ++--
 arch/x86/kernel/relocate_kernel_64.S  | 4 ++--
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 38f17a1..f899717 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 c9b2ba7..240d761 100644
--- a/arch/x86/include/asm/vdso/processor.h
+++ b/arch/x86/include/asm/vdso/processor.h
@@ -7,10 +7,10 @@
 
 #ifndef __ASSEMBLER__
 
-/* REP NOP (PAUSE) is a good thing to insert into busy-wait loops. */
+/* 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 1d63552..ea604f4 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: