diff -r 09ee974e722f xen/drivers/passthrough/amd/iommu_init.c
--- a/xen/drivers/passthrough/amd/iommu_init.c	Thu Jul 31 13:37:29 2008 +0100
+++ b/xen/drivers/passthrough/amd/iommu_init.c	Thu Jul 31 15:34:03 2008 +0200
@@ -477,7 +477,10 @@ void __init enable_iommu(struct amd_iomm
     spin_lock_irqsave(&iommu->lock, flags);
 
     if ( iommu->enabled )
-        return;
+    {
+       spin_unlock_irqrestore(&iommu->lock, flags); 
+       return;
+    }
 
     iommu->dev_table.alloc_size = device_table.alloc_size;
     iommu->dev_table.entries = device_table.entries;