KVM: x86: Initialize number of APIC LVT entries during APIC creation

Initialize the number of LVT entries during APIC creation, else the field
will be incorrectly left '0' if userspace never invokes KVM_X86_SETUP_MCE.

Add and use a helper to calculate the number of entries even though
MCG_CMCI_P is not set by default in vcpu->arch.mcg_cap.  Relying on that
to always be true is unnecessarily risky, and subtle/confusing as well.

Fixes: 4b903561ec ("KVM: x86: Add Corrected Machine Check Interrupt (CMCI) emulation to lapic.")
Reported-by: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Jue Wang <juew@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/lapic.c

@@ -405,6 +405,11 @@ static inline bool kvm_lapic_lvt_supported(struct kvm_lapic *apic, int lvt_index
 	return apic->nr_lvt_entries > lvt_index;
 }
 
+static inline int kvm_apic_calc_nr_lvt_entries(struct kvm_vcpu *vcpu)
+{
+	return KVM_APIC_MAX_NR_LVT_ENTRIES - !(vcpu->arch.mcg_cap & MCG_CMCI_P);
+}
+
 void kvm_apic_set_version(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
@@ -2561,6 +2566,8 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
 	}
 	apic->vcpu = vcpu;
 
+	apic->nr_lvt_entries = kvm_apic_calc_nr_lvt_entries(vcpu);
+
 	hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC,
 		     HRTIMER_MODE_ABS_HARD);
 	apic->lapic_timer.timer.function = apic_timer_fn;