linux-kernel - [PATCH v2 2/2] KVM: x86: Remove redundant vm_entry_controls

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Date:   Fri, 11 Mar 2022 18:26:43 +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 v2 2/2] 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.

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 | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index cadb3769031c..70717f56a2a2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2907,7 +2907,6 @@ 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