iommu/vt-d: Handle race between registration and device probe

Currently we rely on registering all our instances before initially
allowing any .probe_device calls via bus_set_iommu(). In preparation for
phasing out the latter, make sure we won't inadvertently return success
for a device associated with a known but not yet registered instance,
otherwise we'll run straight into iommu_group_get_for_dev() trying to
use NULL ops.

That also highlights an issue with intel_iommu_get_resv_regions() taking
dmar_global_lock from within a section where intel_iommu_init() already
holds it, which already exists via probe_acpi_namespace_devices() when
an ANDD device is probed, but gets more obvious with the upcoming change
to iommu_device_register(). Since they are both read locks it manages
not to deadlock in practice, and a more in-depth rework of this locking
is underway, so no attempt is made to address it here.
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/579f2692291bcbfc3ac64f7456fcff0d629af131.1660572783.git.robin.murphy@arm.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/iommu.c

@@ -4449,7 +4449,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev)
 	u8 bus, devfn;
 
 	iommu = device_to_iommu(dev, &bus, &devfn);
-	if (!iommu)
+	if (!iommu || !iommu->iommu.ops)
 		return ERR_PTR(-ENODEV);
 
 	info = kzalloc(sizeof(*info), GFP_KERNEL);