linux-kernel - [PATCH] x86/boot: Avoid writing to cr4 twice in startup

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Message-ID: <20250618082717.1098-1-khaliidcaliy@gmail.com>
Date: Wed, 18 Jun 2025 08:26:33 +0000
From: Khalid Ali <khaliidcaliy@...il.com>
To: tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org
Cc: hpa@...or.com,
	linux-kernel@...r.kernel.org,
	Khalid Ali <khaliidcaliy@...il.com>
Subject: [PATCH] x86/boot: Avoid writing to cr4 twice in startup_64()

From: Khalid Ali <khaliidcaliy@...il.com>

When Initializing cr4 bit PSE and PGE, cr4 is written twice for	
each bit.

Instead, set both bits first and write CR4 once, avoiding redundant
writes.

Signed-off-by: Khalid Ali <khaliidcaliy@...il.com>
---
 arch/x86/kernel/head_64.S | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4390a28f7dad..dfb5390e5c9a 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -222,12 +222,9 @@ SYM_INNER_LABEL(common_startup_64, SYM_L_LOCAL)
 
 	/* Even if ignored in long mode, set PSE uniformly on all logical CPUs. */
 	btsl	$X86_CR4_PSE_BIT, %ecx
-	movq	%rcx, %cr4
-
-	/*
-	 * Set CR4.PGE to re-enable global translations.
-	 */
+	/* Set CR4.PGE to re-enable global translations. */
 	btsl	$X86_CR4_PGE_BIT, %ecx
+	
 	movq	%rcx, %cr4
 
 #ifdef CONFIG_SMP
-- 
2.49.0