diff -r 7fe15a0ee3d8 xen/drivers/passthrough/vtd/iommu.h
--- a/xen/drivers/passthrough/vtd/iommu.h	Tue Feb 17 11:20:18 2009 +0000
+++ b/xen/drivers/passthrough/vtd/iommu.h	Tue Feb 17 18:18:31 2009 -0800
@@ -397,8 +397,8 @@ struct poll_info {
     u32 udata;
 };
 
-#define MAX_QINVAL_PAGES 8
 #define NUM_QINVAL_PAGES 1
+#define IQA_REG_QS       0    // derived from NUM_QINVAL_PAGES per VT-d spec.
 #define QINVAL_ENTRY_NR (PAGE_SIZE_4K*NUM_QINVAL_PAGES/sizeof(struct qinval_entry))
 #define qinval_present(v) ((v).lo & 1)
 #define qinval_fault_disable(v) (((v).lo >> 1) & 1)
diff -r 7fe15a0ee3d8 xen/drivers/passthrough/vtd/qinval.c
--- a/xen/drivers/passthrough/vtd/qinval.c	Tue Feb 17 11:20:18 2009 +0000
+++ b/xen/drivers/passthrough/vtd/qinval.c	Tue Feb 17 18:05:25 2009 -0800
@@ -445,8 +445,7 @@ int qinval_setup(struct iommu *iommu)
      * registers are automatically reset to 0 with write
      * to IQA register.
      */
-    if ( NUM_QINVAL_PAGES <= MAX_QINVAL_PAGES )
-        qi_ctrl->qinval_maddr |= NUM_QINVAL_PAGES - 1;
+    qi_ctrl->qinval_maddr |= IQA_REG_QS;
     dmar_writeq(iommu->reg, DMAR_IQA_REG, qi_ctrl->qinval_maddr);
 
     /* enable queued invalidation hardware */