diff -buNr a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
--- a/xen/arch/x86/hvm/emulate.c	2008-08-20 10:41:21.348398020 +0100
+++ b/xen/arch/x86/hvm/emulate.c	2008-08-20 12:32:22.603556476 +0100
@@ -246,7 +246,7 @@
     }
 
     /* If the range does not straddle a page boundary then we're done. */
-    done = reverse ? bytes_per_rep + (addr & ~PAGE_MASK) : -addr & ~PAGE_MASK;
+    done = reverse ? -addr & ~PAGE_MASK : bytes_per_rep + (addr & ~PAGE_MASK);
     todo = *reps * bytes_per_rep;
     if ( done >= todo )
         goto done;