VT-d: properly reserve DID 0 for caching mode IOMMUs

Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
still have DID 0 allocated to it, because of the zero-filling of
domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
used.

Fixes: b9c20c78789f ("VT-d: per-iommu domain-id")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 5de9a73f56fedb21f3496cf09d53f34a47ca8bc8..643db07cf0af06a37b86db9ca30648379fef082c 100644 (file)
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1259,16 +1259,19 @@ int __init iommu_alloc(struct acpi_drhd_unit *drhd)
     if ( !iommu->domid_bitmap )
         return -ENOMEM;
 
+    iommu->domid_map = xzalloc_array(u16, nr_dom);
+    if ( !iommu->domid_map )
+        return -ENOMEM;
+
     /*
-     * if Caching mode is set, then invalid translations are tagged with
-     * domain id 0, Hence reserve bit 0 for it
+     * If Caching mode is set, then invalid translations are tagged with
+     * domain id 0. Hence reserve bit/slot 0.
      */
     if ( cap_caching_mode(iommu->cap) )
+    {
+        iommu->domid_map[0] = DOMID_INVALID;
         __set_bit(0, iommu->domid_bitmap);
-
-    iommu->domid_map = xzalloc_array(u16, nr_dom);
-    if ( !iommu->domid_map )
-        return -ENOMEM;
+    }
 
     return 0;
 }