KVM: x86: Remove redundant vm_entry_controls_clearbit() call

When emulating exit from long mode, EFER_LMA is cleared with
vmx_set_efer().  This will already unset the VM_ENTRY_IA32E_MODE control
bit as requested by SDM, so there is no need to unset VM_ENTRY_IA32E_MODE
again in exit_lmode() explicitly.  In case EFER isn't supported by
hardware, long mode isn't supported, so exit_lmode() cannot be reached.

Note that, thanks to the shadow controls mechanism, this change doesn't
eliminate vmread or vmwrite.

Signed-off-by: Zhenzhong Duan <[email protected]>
Message-Id: <20220311102643[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2d122416b1e87ca5a47084013b475a780b02b46f..04d170c4b61eb48688b85d60b961d5b539509cb4 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2902,7 +2902,6 @@ 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);
 }