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_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
				       gva_t addr, void *val,
				       unsigned int bytes,
				       struct x86_exception *exception)
{
	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
	void *data = val;
	int r = X86EMUL_CONTINUE;

	while (bytes) {
		gpa_t gpa =  vcpu->arch.walk_mmu->gva_to_gpa(vcpu, addr,
							     PFERR_WRITE_MASK,
							     exception);
		unsigned offset = addr & (PAGE_SIZE-1);
		unsigned towrite = min(bytes, (unsigned)PAGE_SIZE - offset);
		int ret;

		if (gpa == UNMAPPED_GVA)
			return X86EMUL_PROPAGATE_FAULT;
		ret = kvm_write_guest(vcpu->kvm, gpa, data, towrite);
		if (ret < 0) {
			r = X86EMUL_IO_NEEDED;
			goto out;
		}

		bytes -= towrite;
		data += towrite;
		addr += towrite;
	}
out:
	return r;
}

int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
				       gva_t addr, void *val,
				       unsigned int bytes,
				       struct x86_exception *exception)
{
	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
	void *data = val;
	int r = X86EMUL_CONTINUE;

	while (bytes) {
		gpa_t gpa =  vcpu->arch.walk_mmu->gva_to_gpa(vcpu, addr,
							     PFERR_WRITE_MASK,
							     exception);
		unsigned offset = addr & (PAGE_SIZE-1);
		unsigned towrite = min(bytes, (unsigned)PAGE_SIZE - offset);
		int ret;

		if (gpa == UNMAPPED_GVA)
			return X86EMUL_PROPAGATE_FAULT;
		ret = kvm_write_guest(vcpu->kvm, gpa, data, towrite);
		if (ret < 0) {
			r = X86EMUL_IO_NEEDED;
			goto out;
		}

		bytes -= towrite;
		data += towrite;
		addr += towrite;
	}
out:
	return r;
}
