KVM: x86: hyper-v: Prepare to meet unallocated Hyper-V context

Currently, Hyper-V context is part of 'struct kvm_vcpu_arch' and is always
available. As a preparation to allocating it dynamically, check that it is
not NULL at call sites which can normally proceed without it i.e. the
behavior is identical to the situation when Hyper-V emulation is not being
used by the guest.

When Hyper-V context for a particular vCPU is not allocated, we may still
need to get 'vp_index' from there. E.g. in a hypothetical situation when
Hyper-V emulation was enabled on one CPU and wasn't on another, Hyper-V
style send-IPI hypercall may still be used. Luckily, vp_index is always
initialized to kvm_vcpu_get_idx() and can only be changed when Hyper-V
context is present. Introduce kvm_hv_get_vpindex() helper for
simplification.

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/kvm/hyperv.c

···
 		return NULL;
 
 	vcpu = kvm_get_vcpu(kvm, vpidx);
-	if (vcpu && to_hv_vcpu(vcpu)->vp_index == vpidx)
+	if (vcpu && kvm_hv_get_vpindex(vcpu) == vpidx)
 		return vcpu;
 	kvm_for_each_vcpu(i, vcpu, kvm)
-		if (to_hv_vcpu(vcpu)->vp_index == vpidx)
+		if (kvm_hv_get_vpindex(vcpu) == vpidx)
 			return vcpu;
 	return NULL;
 }
···
 		break;
 	}
 
-	trace_kvm_hv_syndbg_get_msr(vcpu->vcpu_id,
-				    to_hv_vcpu(vcpu)->vp_index, msr,
-				    *pdata);
+	trace_kvm_hv_syndbg_get_msr(vcpu->vcpu_id, kvm_hv_get_vpindex(vcpu), msr, *pdata);
 
 	return 0;
 }
···
 	u64 time_now, exp_time;
 	int i;
 
+	if (!hv_vcpu)
+		return;
+
 	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
 		if (test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap)) {
 			stimer = &hv_vcpu->stimer[i];
···
 bool kvm_hv_assist_page_enabled(struct kvm_vcpu *vcpu)
 {
 	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+	if (!hv_vcpu)
+		return false;
 
 	if (!(hv_vcpu->hv_vapic & HV_X64_MSR_VP_ASSIST_PAGE_ENABLE))
 		return false;
···
 
 	bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS);
 	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (test_bit(to_hv_vcpu(vcpu)->vp_index,
-			     (unsigned long *)vp_bitmap))
+		if (test_bit(kvm_hv_get_vpindex(vcpu), (unsigned long *)vp_bitmap))
 			__set_bit(i, vcpu_bitmap);
 	}
 	return vcpu_bitmap;

arch/x86/kvm/hyperv.h

···
 	return &vcpu->kvm->arch.hyperv.hv_syndbg;
 }
 
+static inline u32 kvm_hv_get_vpindex(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+	return hv_vcpu ? hv_vcpu->vp_index : kvm_vcpu_get_idx(vcpu);
+}
+
 int kvm_hv_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host);
 int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host);
 
···
 static inline bool kvm_hv_has_stimer_pending(struct kvm_vcpu *vcpu)
 {
 	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+	if (!hv_vcpu)
+		return false;
 
 	return !bitmap_empty(hv_vcpu->stimer_pending_bitmap,
 			     HV_SYNIC_STIMER_COUNT);

arch/x86/kvm/lapic.c

···
 	apic_clear_isr(vector, apic);
 	apic_update_ppr(apic);
 
-	if (test_bit(vector, to_hv_synic(apic->vcpu)->vec_bitmap))
+	if (to_hv_vcpu(apic->vcpu) &&
+	    test_bit(vector, to_hv_synic(apic->vcpu)->vec_bitmap))
 		kvm_hv_synic_send_eoi(apic->vcpu, vector);
 
 	kvm_ioapic_send_eoi(apic, vector);
···
 	 */
 
 	apic_clear_irr(vector, apic);
-	if (test_bit(vector, to_hv_synic(vcpu)->auto_eoi_bitmap)) {
+	if (to_hv_vcpu(vcpu) && test_bit(vector, to_hv_synic(vcpu)->auto_eoi_bitmap)) {
 		/*
 		 * For auto-EOI interrupts, there might be another pending
 		 * interrupt above PPR, so check whether to raise another

arch/x86/kvm/vmx/vmx.c

···
 
 	/* All fields are clean at this point */
 	if (static_branch_unlikely(&enable_evmcs)) {
-		struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
-
 		current_evmcs->hv_clean_fields |=
 			HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
 
-		current_evmcs->hv_vp_id = hv_vcpu->vp_index;
+		current_evmcs->hv_vp_id = kvm_hv_get_vpindex(vcpu);
 	}
 
 	/* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */

arch/x86/kvm/x86.c

···
 	if (!kvm_apic_hw_enabled(vcpu->arch.apic))
 		return;
 
-	bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
-		  to_hv_synic(vcpu)->vec_bitmap, 256);
+	if (to_hv_vcpu(vcpu))
+		bitmap_or((ulong *)eoi_exit_bitmap,
+			  vcpu->arch.ioapic_handled_vectors,
+			  to_hv_synic(vcpu)->vec_bitmap, 256);
+
 	static_call(kvm_x86_load_eoi_exitmap)(vcpu, eoi_exit_bitmap);
 }