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 int kvm_sn2_setup_mappings(struct kvm_vcpu *vcpu)
{
	unsigned long pte, rtc_phys_addr, map_addr;
	int slot;

	map_addr = KVM_VMM_BASE + (1UL << KVM_VMM_SHIFT);
	rtc_phys_addr = LOCAL_MMR_OFFSET | SH_RTC;
	pte = pte_val(mk_pte_phys(rtc_phys_addr, PAGE_KERNEL_UC));
	slot = ia64_itr_entry(0x3, map_addr, pte, PAGE_SHIFT);
	vcpu->arch.sn_rtc_tr_slot = slot;
	if (slot < 0) {
		printk(KERN_ERR "Mayday mayday! RTC mapping failed!\n");
		slot = 0;
	}
	return slot;
}

static int kvm_sn2_setup_mappings(struct kvm_vcpu *vcpu)
{
	unsigned long pte, rtc_phys_addr, map_addr;
	int slot;

	map_addr = KVM_VMM_BASE + (1UL << KVM_VMM_SHIFT);
	rtc_phys_addr = LOCAL_MMR_OFFSET | SH_RTC;
	pte = pte_val(mk_pte_phys(rtc_phys_addr, PAGE_KERNEL_UC));
	slot = ia64_itr_entry(0x3, map_addr, pte, PAGE_SHIFT);
	vcpu->arch.sn_rtc_tr_slot = slot;
	if (slot < 0) {
		printk(KERN_ERR "Mayday mayday! RTC mapping failed!\n");
		slot = 0;
	}
	return slot;
}
