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 kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
					       struct kvm_vcpu_events *events)
{
	process_nmi(vcpu);
	events->exception.injected =
		vcpu->arch.exception.pending &&
		!kvm_exception_is_soft(vcpu->arch.exception.nr);
	events->exception.nr = vcpu->arch.exception.nr;
	events->exception.has_error_code = vcpu->arch.exception.has_error_code;
	events->exception.pad = 0;
	events->exception.error_code = vcpu->arch.exception.error_code;

	events->interrupt.injected =
		vcpu->arch.interrupt.pending && !vcpu->arch.interrupt.soft;
	events->interrupt.nr = vcpu->arch.interrupt.nr;
	events->interrupt.soft = 0;
	events->interrupt.shadow =
		kvm_x86_ops->get_interrupt_shadow(vcpu,
			KVM_X86_SHADOW_INT_MOV_SS | KVM_X86_SHADOW_INT_STI);

	events->nmi.injected = vcpu->arch.nmi_injected;
	events->nmi.pending = vcpu->arch.nmi_pending != 0;
	events->nmi.masked = kvm_x86_ops->get_nmi_mask(vcpu);
	events->nmi.pad = 0;

	events->sipi_vector = vcpu->arch.sipi_vector;

	events->flags = (KVM_VCPUEVENT_VALID_NMI_PENDING
			 | KVM_VCPUEVENT_VALID_SIPI_VECTOR
			 | KVM_VCPUEVENT_VALID_SHADOW);
	memset(&events->reserved, 0, sizeof(events->reserved));
}

static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
					       struct kvm_vcpu_events *events)
{
	process_nmi(vcpu);
	events->exception.injected =
		vcpu->arch.exception.pending &&
		!kvm_exception_is_soft(vcpu->arch.exception.nr);
	events->exception.nr = vcpu->arch.exception.nr;
	events->exception.has_error_code = vcpu->arch.exception.has_error_code;
	events->exception.pad = 0;
	events->exception.error_code = vcpu->arch.exception.error_code;

	events->interrupt.injected =
		vcpu->arch.interrupt.pending && !vcpu->arch.interrupt.soft;
	events->interrupt.nr = vcpu->arch.interrupt.nr;
	events->interrupt.soft = 0;
	events->interrupt.shadow =
		kvm_x86_ops->get_interrupt_shadow(vcpu,
			KVM_X86_SHADOW_INT_MOV_SS | KVM_X86_SHADOW_INT_STI);

	events->nmi.injected = vcpu->arch.nmi_injected;
	events->nmi.pending = vcpu->arch.nmi_pending != 0;
	events->nmi.masked = kvm_x86_ops->get_nmi_mask(vcpu);
	events->nmi.pad = 0;

	events->sipi_vector = vcpu->arch.sipi_vector;

	events->flags = (KVM_VCPUEVENT_VALID_NMI_PENDING
			 | KVM_VCPUEVENT_VALID_SIPI_VECTOR
			 | KVM_VCPUEVENT_VALID_SHADOW);
	memset(&events->reserved, 0, sizeof(events->reserved));
}
