KVM: x86: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

This patch fixes the following warnings:

arch/x86/kvm/lapic.c:1037:27: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/lapic.c:1876:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/hyperv.c:1637:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/svm.c:4396:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/mmu.c:4372:36: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/x86.c:3835:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/x86.c:7938:23: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/vmx/vmx.c:2015:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kvm/vmx/vmx.c:1773:6: warning: this statement may fall through [-Wimplicit-fallthrough=]

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enabling -Wimplicit-fallthrough.

Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/kvm/hyperv.c

···
 		ret = kvm_hvcall_signal_event(vcpu, fast, ingpa);
 		if (ret != HV_STATUS_INVALID_PORT_ID)
 			break;
-		/* maybe userspace knows this conn_id: fall through */
+		/* fall through - maybe userspace knows this conn_id. */
 	case HVCALL_POST_MESSAGE:
 		/* don't bother userspace if it has no way to handle it */
 		if (unlikely(rep || !vcpu_to_synic(vcpu)->active)) {

arch/x86/kvm/lapic.c

···
 	switch (delivery_mode) {
 	case APIC_DM_LOWEST:
 		vcpu->arch.apic_arb_prio++;
+		/* fall through */
 	case APIC_DM_FIXED:
 		if (unlikely(trig_mode && !level))
 			break;
···
 
 	case APIC_LVT0:
 		apic_manage_nmi_watchdog(apic, val);
+		/* fall through */
 	case APIC_LVTTHMR:
 	case APIC_LVTPC:
 	case APIC_LVT1:

arch/x86/kvm/mmu.c

···
 			rsvd_bits(maxphyaddr, 51);
 		rsvd_check->rsvd_bits_mask[1][4] =
 			rsvd_check->rsvd_bits_mask[0][4];
+		/* fall through */
 	case PT64_ROOT_4LEVEL:
 		rsvd_check->rsvd_bits_mask[0][3] = exb_bit_rsvd |
 			nonleaf_bit8_rsvd | rsvd_bits(7, 7) |

arch/x86/kvm/svm.c

···
 	case MSR_IA32_APICBASE:
 		if (kvm_vcpu_apicv_active(vcpu))
 			avic_update_vapic_bar(to_svm(vcpu), data);
-		/* Follow through */
+		/* Fall through */
 	default:
 		return kvm_set_msr_common(vcpu, msr);
 	}

arch/x86/kvm/vmx/vmx.c

···
 		if (!msr_info->host_initiated &&
 		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
 			return 1;
-		/* Otherwise falls through */
+		/* Else, falls through */
 	default:
 		msr = find_msr_entry(vmx, msr_info->index);
 		if (msr) {
···
 		/* Check reserved bit, higher 32 bits should be zero */
 		if ((data >> 32) != 0)
 			return 1;
-		/* Otherwise falls through */
+		/* Else, falls through */
 	default:
 		msr = find_msr_entry(vmx, msr_index);
 		if (msr) {

arch/x86/kvm/x86.c

···
 	case KVM_CAP_HYPERV_SYNIC2:
 		if (cap->args[0])
 			return -EINVAL;
+		/* fall through */
+
 	case KVM_CAP_HYPERV_SYNIC:
 		if (!irqchip_in_kernel(vcpu->kvm))
 			return -EINVAL;
···
 		vcpu->arch.pv.pv_unhalted = false;
 		vcpu->arch.mp_state =
 			KVM_MP_STATE_RUNNABLE;
+		/* fall through */
 	case KVM_MP_STATE_RUNNABLE:
 		vcpu->arch.apf.halted = false;
 		break;