KVM: Ensure all vcpus are consistent with in-kernel irqchip settings

(cherry picked from commit 3e515705a1f46beb1c942bb8043c16f8ac7b1e9e)

If some vcpus are created before KVM_CREATE_IRQCHIP, then
irqchip_in_kernel() and vcpu->arch.apic will be inconsistent, leading
to potential NULL pointer dereferences.

Fix by:
- ensuring that no vcpus are installed when KVM_CREATE_IRQCHIP is called
- ensuring that a vcpu has an apic if it is installed after KVM_CREATE_IRQCHIP

This is somewhat long winded because vcpu->arch.apic is created without
kvm->lock held.

Based on earlier patch by Michael Ellerman.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
int kvm_arch_hardware_enable(void *garbage)
{
	struct kvm *kvm;
	struct kvm_vcpu *vcpu;
	int i;

	kvm_shared_msr_cpu_online();
	list_for_each_entry(kvm, &vm_list, vm_list)
		kvm_for_each_vcpu(i, vcpu, kvm)
			if (vcpu->cpu == smp_processor_id())
				kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
	return kvm_x86_ops->hardware_enable(garbage);
}

int kvm_arch_hardware_enable(void *garbage)
{
	struct kvm *kvm;
	struct kvm_vcpu *vcpu;
	int i;

	kvm_shared_msr_cpu_online();
	list_for_each_entry(kvm, &vm_list, vm_list)
		kvm_for_each_vcpu(i, vcpu, kvm)
			if (vcpu->cpu == smp_processor_id())
				kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
	return kvm_x86_ops->hardware_enable(garbage);
}
