linux-kernel - [PATCH] KVM: x86: Remove redundant vm_entry_controls

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Date:   Thu, 10 Mar 2022 19:13:54 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...el.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org
Subject: [PATCH] KVM: x86: Remove redundant vm_entry_controls_clearbit() call

When emulating exit from long mode, EFER_LMA is cleared which lead to
efer writing emulation, which will unset VM_ENTRY_IA32E_MODE control
bit as requested by SDM. So no need to unset VM_ENTRY_IA32E_MODE again
in exit_lmode() explicitly.

In fact benefited from shadow controls mechanism, this change doesn't
eliminate vmread or vmwrite.

Opportunistically remove unnecessory assignment to uret MSR data field
as vmx_setup_uret_msrs() will do the same thing.

In case EFER isn't supported by hardware, long mode isn't supported,
so this will no break.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...el.com>
---
 arch/x86/kvm/vmx/vmx.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b730d799c26e..b04588dc7faa 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2878,14 +2878,11 @@ int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 		return 0;
 
 	vcpu->arch.efer = efer;
-	if (efer & EFER_LMA) {
+	if (efer & EFER_LMA)
 		vm_entry_controls_setbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE);
-		msr->data = efer;
-	} else {
+	else
 		vm_entry_controls_clearbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE);
 
-		msr->data = efer & ~EFER_LME;
-	}
 	vmx_setup_uret_msrs(vmx);
 	return 0;
 }
@@ -2911,7 +2908,6 @@ static void enter_lmode(struct kvm_vcpu *vcpu)
 
 static void exit_lmode(struct kvm_vcpu *vcpu)
 {
-	vm_entry_controls_clearbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE);
 	vmx_set_efer(vcpu, vcpu->arch.efer & ~EFER_LMA);
 }
 
-- 
2.25.1