[<prev] [next>] [day] [month] [year] [list]
Message-ID: <20250807063733.6943-1-ubizjak@gmail.com>
Date: Thu, 7 Aug 2025 08:36:51 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: kvm@...r.kernel.org,
x86@...nel.org,
linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.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] KVM: VMX: Micro-optimize SPEC_CTRL handling in __vmx_vcpu_run()
Use memory operand in CMP instruction to avoid usage of a
temporary register. Use %eax register to hold VMX_spec_ctrl
and use it directly in the follow-up WRMSR.
The new code saves a few bytes by removing two MOV insns, from:
2d: 48 8b 7c 24 10 mov 0x10(%rsp),%rdi
32: 8b bf 48 18 00 00 mov 0x1848(%rdi),%edi
38: 65 8b 35 00 00 00 00 mov %gs:0x0(%rip),%esi
3f: 39 fe cmp %edi,%esi
41: 74 0b je 4e <...>
43: b9 48 00 00 00 mov $0x48,%ecx
48: 31 d2 xor %edx,%edx
4a: 89 f8 mov %edi,%eax
4c: 0f 30 wrmsr
to:
2d: 48 8b 7c 24 10 mov 0x10(%rsp),%rdi
32: 8b 87 48 18 00 00 mov 0x1848(%rdi),%eax
38: 65 3b 05 00 00 00 00 cmp %gs:0x0(%rip),%eax
3f: 74 09 je 4a <...>
41: b9 48 00 00 00 mov $0x48,%ecx
46: 31 d2 xor %edx,%edx
48: 0f 30 wrmsr
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.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/kvm/vmx/vmenter.S | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 0a6cf5bff2aa..c65de5de92ab 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -118,13 +118,11 @@ SYM_FUNC_START(__vmx_vcpu_run)
* and vmentry.
*/
mov 2*WORD_SIZE(%_ASM_SP), %_ASM_DI
- movl VMX_spec_ctrl(%_ASM_DI), %edi
- movl PER_CPU_VAR(x86_spec_ctrl_current), %esi
- cmp %edi, %esi
+ movl VMX_spec_ctrl(%_ASM_DI), %eax
+ cmp PER_CPU_VAR(x86_spec_ctrl_current), %eax
je .Lspec_ctrl_done
mov $MSR_IA32_SPEC_CTRL, %ecx
xor %edx, %edx
- mov %edi, %eax
wrmsr
.Lspec_ctrl_done:
--
2.50.1
Powered by blists - more mailing lists