Commit 6dad5912 authored Feb 11, 2026 by Uros Bizjak Committed by Sean Christopherson Mar 02, 2026

KVM: VMX: Drop obsolete branch hint prefixes from inline asm



Remove explicit branch hint prefixes (.byte 0x2e / 0x3e) from VMX
inline assembly sequences.

These prefixes (CS/DS segment overrides used as branch hints on
very old x86 CPUs) have been ignored by modern processors for a
long time. Keeping them provides no measurable benefit and only
enlarges the generated code.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://patch.msgid.link/20260211102928.100944-1-ubizjak@gmail.com


Signed-off-by: Sean Christopherson <seanjc@google.com>

parent 11439c46

arch/x86/kvm/vmx/vmx_ops.h

+0 −3

Original line number	Diff line number	Diff line
		@@ -119,7 +119,6 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
		#else /* !CONFIG_CC_HAS_ASM_GOTO_OUTPUT */

		asm volatile("1: vmread %[field], %[output]\n\t"
		".byte 0x3e\n\t" /* branch taken hint */
		"ja 3f\n\t"

		/*
		@@ -191,7 +190,6 @@ static __always_inline unsigned long vmcs_readl(unsigned long field)
		#define vmx_asm1(insn, op1, error_args...) \
		do { \
		asm goto("1: " __stringify(insn) " %0\n\t" \
		".byte 0x2e\n\t" /* branch not taken hint */ \
		"jna %l[error]\n\t" \
		_ASM_EXTABLE(1b, %l[fault]) \
		: : op1 : "cc" : error, fault); \
		@@ -208,7 +206,6 @@ fault: \
		#define vmx_asm2(insn, op1, op2, error_args...) \
		do { \
		asm goto("1: " __stringify(insn) " %1, %0\n\t" \
		".byte 0x2e\n\t" /* branch not taken hint */ \
		"jna %l[error]\n\t" \
		_ASM_EXTABLE(1b, %l[fault]) \
		: : op1, op2 : "cc" : error, fault); \