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>
static void vcpu_global_purge(void *info)
{
	struct call_data *p = (struct call_data *)info;
	struct kvm_vcpu *vcpu = p->vcpu;

	if (test_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests))
		return;

	set_bit(KVM_REQ_PTC_G, &vcpu->requests);
	if (vcpu->arch.ptc_g_count < MAX_PTC_G_NUM) {
		vcpu->arch.ptc_g_data[vcpu->arch.ptc_g_count++] =
							p->ptc_g_data;
	} else {
		clear_bit(KVM_REQ_PTC_G, &vcpu->requests);
		vcpu->arch.ptc_g_count = 0;
		set_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests);
	}
}

static void vcpu_global_purge(void *info)
{
	struct call_data *p = (struct call_data *)info;
	struct kvm_vcpu *vcpu = p->vcpu;

	if (test_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests))
		return;

	set_bit(KVM_REQ_PTC_G, &vcpu->requests);
	if (vcpu->arch.ptc_g_count < MAX_PTC_G_NUM) {
		vcpu->arch.ptc_g_data[vcpu->arch.ptc_g_count++] =
							p->ptc_g_data;
	} else {
		clear_bit(KVM_REQ_PTC_G, &vcpu->requests);
		vcpu->arch.ptc_g_count = 0;
		set_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests);
	}
}
