AMD/IOMMU: let callers of amd_iommu_alloc_intremap_table() handle errors

Additional users of the function will want to handle errors more
gracefully. Remove the BUG_ON()s and make the current caller panic()
instead.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v5: New.

--- a/xen/drivers/passthrough/amd/iommu_acpi.c
+++ b/xen/drivers/passthrough/amd/iommu_acpi.c
@@ -86,6 +86,10 @@ static void __init add_ivrs_mapping_entr
              ivrs_mappings[alias_id].intremap_table = shared_intremap_table;
              ivrs_mappings[alias_id].intremap_inuse = shared_intremap_inuse;
          }
+
+         if ( !ivrs_mappings[alias_id].intremap_table )
+             panic("No memory for %04x:%02x:%02x.%u's IRT\n", iommu->seg,
+                   PCI_BUS(alias_id), PCI_SLOT(alias_id), PCI_FUNC(alias_id));
     }
 
     ivrs_mappings[alias_id].valid = true;
--- a/xen/drivers/passthrough/amd/iommu_intr.c
+++ b/xen/drivers/passthrough/amd/iommu_intr.c
@@ -817,12 +817,22 @@ int __init amd_iommu_free_intremap_table
 void *__init amd_iommu_alloc_intremap_table(
     const struct amd_iommu *iommu, unsigned long **inuse_map)
 {
-    void *tb = __alloc_amd_iommu_tables(intremap_table_order(iommu));
+    unsigned int order = intremap_table_order(iommu);
+    void *tb = __alloc_amd_iommu_tables(order);
+
+    if ( tb )
+    {
+        *inuse_map = xzalloc_array(unsigned long,
+                                   BITS_TO_LONGS(INTREMAP_ENTRIES));
+        if ( *inuse_map )
+            memset(tb, 0, PAGE_SIZE << order);
+        else
+        {
+            __free_amd_iommu_tables(tb, order);
+            tb = NULL;
+        }
+    }
 
-    BUG_ON(tb == NULL);
-    memset(tb, 0, PAGE_SIZE << intremap_table_order(iommu));
-    *inuse_map = xzalloc_array(unsigned long, BITS_TO_LONGS(INTREMAP_ENTRIES));
-    BUG_ON(*inuse_map == NULL);
     return tb;
 }