vfio: Check that IOMMU MR translates to system address space

At the moment IOMMU MR only translate to the system memory.
However if some new code changes this, we will need clear indication why
it is not working so here is the check.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

hw/vfio/common.c

@@ -269,6 +269,12 @@ static void vfio_iommu_map_notify(Notifier *n, void *data)
 
     trace_vfio_iommu_map_notify(iova, iova + iotlb->addr_mask);
 
+    if (iotlb->target_as != &address_space_memory) {
+        error_report("Wrong target AS \"%s\", only system memory is allowed",
+                     iotlb->target_as->name ? iotlb->target_as->name : "none");
+        return;
+    }
+
     /*
      * The IOMMU TLB entry we have just covers translation through
      * this IOMMU to its immediate target.  We need to translate