arm64: KVM: Always set ICH_HCR_EL2.EN if GICv4 is enabled

The normal interrupt flow is not to enable the vgic when no virtual
interrupt is to be injected (i.e. the LRs are empty). But when a guest
is likely to use GICv4 for LPIs, we absolutely need to switch it on
at all times. Otherwise, VLPIs only get delivered when there is something
in the LRs, which doesn't happen very often.
Reported-by: Nianyao Tang <tangnianyao@huawei.com>
Tested-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

virt/kvm/arm/hyp/vgic-v3-sr.c

@@ -222,7 +222,7 @@ void __hyp_text __vgic_v3_save_state(struct kvm_vcpu *vcpu)
 		}
 	}
 
-	if (used_lrs) {
+	if (used_lrs || cpu_if->its_vpe.its_vm) {
 		int i;
 		u32 elrsr;
 
@@ -247,7 +247,7 @@ void __hyp_text __vgic_v3_restore_state(struct kvm_vcpu *vcpu)
 	u64 used_lrs = vcpu->arch.vgic_cpu.used_lrs;
 	int i;
 
-	if (used_lrs) {
+	if (used_lrs || cpu_if->its_vpe.its_vm) {
 		write_gicreg(cpu_if->vgic_hcr, ICH_HCR_EL2);
 
 		for (i = 0; i < used_lrs; i++)

virt/kvm/arm/vgic/vgic.c

@@ -867,15 +867,21 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
 	 * either observe the new interrupt before or after doing this check,
 	 * and introducing additional synchronization mechanism doesn't change
 	 * this.
+	 *
+	 * Note that we still need to go through the whole thing if anything
+	 * can be directly injected (GICv4).
 	 */
-	if (list_empty(&vcpu->arch.vgic_cpu.ap_list_head))
+	if (list_empty(&vcpu->arch.vgic_cpu.ap_list_head) &&
+	    !vgic_supports_direct_msis(vcpu->kvm))
 		return;
 
 	DEBUG_SPINLOCK_BUG_ON(!irqs_disabled());
 
-	raw_spin_lock(&vcpu->arch.vgic_cpu.ap_list_lock);
-	vgic_flush_lr_state(vcpu);
-	raw_spin_unlock(&vcpu->arch.vgic_cpu.ap_list_lock);
+	if (!list_empty(&vcpu->arch.vgic_cpu.ap_list_head)) {
+		raw_spin_lock(&vcpu->arch.vgic_cpu.ap_list_lock);
+		vgic_flush_lr_state(vcpu);
+		raw_spin_unlock(&vcpu->arch.vgic_cpu.ap_list_lock);
+	}
 
 	if (can_access_vgic_from_kernel())
 		vgic_restore_state(vcpu);