KVM/Hyper-V/VMX: Add direct tlb flush support

Hyper-V provides direct tlb flush function which helps
L1 Hypervisor to handle Hyper-V tlb flush request from
L2 guest. Add the function support for VMX.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/evmcs.h

@@ -178,6 +178,8 @@ static inline void evmcs_load(u64 phys_addr)
 	struct hv_vp_assist_page *vp_ap =
 		hv_get_vp_assist_page(smp_processor_id());
 
+	if (current_evmcs->hv_enlightenments_control.nested_flush_hypercall)
+		vp_ap->nested_control.features.directhypercall = 1;
 	vp_ap->current_nested_vmcs = phys_addr;
 	vp_ap->enlighten_vmentry = 1;
 }