pseries: Don't allow TCE (iommu) tables to be registered with duplicate LIOBNs

The PAPR specification requires that every bus or device mediated by the
IOMMU have a unique Logical IO Bus Number (LIOBN).  This patch adds a check
to enforce this, which will help catch errors in configuration earlier.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>

hw/spapr_iommu.c

@@ -120,6 +120,12 @@ DMAContext *spapr_tce_new_dma_context(uint32_t liobn, size_t window_size)
 {
     sPAPRTCETable *tcet;
 
+    if (spapr_tce_find_by_liobn(liobn)) {
+        fprintf(stderr, "Attempted to create TCE table with duplicate"
+                " LIOBN 0x%x\n", liobn);
+        return NULL;
+    }
+
     if (!window_size) {
         return NULL;
     }