[PATCH v4 09/12] x86/kvm/nVMX: allow bare VMXON state migration

[Vitaly Kuznetsov <vkuznets@redhat.com>]

It is perfectly valid for a guest to do VMXON and not do VMPTRLD. This
state needs to be preserved on migration.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/vmx.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 377fd91a1a71..6eb86991ca60 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -14132,13 +14132,6 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	if (!page_address_valid(vcpu, kvm_state->vmx.vmxon_pa))
 		return -EINVAL;
 
-	if (kvm_state->size < sizeof(kvm_state) + sizeof(*vmcs12))
-		return -EINVAL;
-
-	if (kvm_state->vmx.vmcs_pa == kvm_state->vmx.vmxon_pa ||
-	    !page_address_valid(vcpu, kvm_state->vmx.vmcs_pa))
-		return -EINVAL;
-
 	if ((kvm_state->vmx.smm.flags & KVM_STATE_NESTED_SMM_GUEST_MODE) &&
 	    (kvm_state->flags & KVM_STATE_NESTED_GUEST_MODE))
 		return -EINVAL;
@@ -14160,6 +14153,14 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	if (ret)
 		return ret;
 
+	/* Empty 'VMXON' state is permitted */
+	if (kvm_state->size < sizeof(kvm_state) + sizeof(*vmcs12))
+		return 0;
+
+	if (kvm_state->vmx.vmcs_pa == kvm_state->vmx.vmxon_pa ||
+	    !page_address_valid(vcpu, kvm_state->vmx.vmcs_pa))
+		return -EINVAL;
+
 	set_current_vmptr(vmx, kvm_state->vmx.vmcs_pa);
 
 	if (kvm_state->vmx.smm.flags & KVM_STATE_NESTED_SMM_VMXON) {
-- 
2.14.4