KVM: nVMX: Reset vmxon_ptr upon VMXOFF emulation.

Currently, 'vmx->nested.vmxon_ptr' is not reset upon VMXOFF
emulation. This is not a problem per se as we never access
it when !vmx->nested.vmxon. But this should be done to avoid
any issue in the future.

Also, initialize the vmxon_ptr when vcpu is created.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Message-Id: <20210929175154.11396-3-yu.c.zhang@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -290,6 +290,7 @@ static void free_nested(struct kvm_vcpu *vcpu)
 
 	vmx->nested.vmxon = false;
 	vmx->nested.smm.vmxon = false;
+	vmx->nested.vmxon_ptr = INVALID_GPA;
 	free_vpid(vmx->nested.vpid02);
 	vmx->nested.posted_intr_nv = -1;
 	vmx->nested.current_vmptr = INVALID_GPA;

arch/x86/kvm/vmx/vmx.c

@@ -6902,6 +6902,7 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 	vcpu_setup_sgx_lepubkeyhash(vcpu);
 
 	vmx->nested.posted_intr_nv = -1;
+	vmx->nested.vmxon_ptr = INVALID_GPA;
 	vmx->nested.current_vmptr = INVALID_GPA;
 	vmx->nested.hv_evmcs_vmptr = EVMPTR_INVALID;