diff --git a/xen/drivers/passthrough/vtd/intremap.c b/xen/drivers/passthrough/vtd/intremap.c
index 1e0317c47a..dfd39c22c1 100644
--- a/xen/drivers/passthrough/vtd/intremap.c
+++ b/xen/drivers/passthrough/vtd/intremap.c
@@ -802,14 +802,15 @@ int enable_intremap(struct iommu *iommu, int eim)
         ir_ctrl->iremap_num = 0;
     }
 
-    /* set extended interrupt mode bit */
-    ir_ctrl->iremap_maddr |= eim ? IRTA_EIME : 0;
-
     spin_lock_irqsave(&iommu->register_lock, flags);
 
-    /* set size of the interrupt remapping table */
-    ir_ctrl->iremap_maddr |= IRTA_REG_TABLE_SIZE;
-    dmar_writeq(iommu->reg, DMAR_IRTA_REG, ir_ctrl->iremap_maddr);
+    /*
+     * Set size of the interrupt remapping table and optionally Extended
+     * Interrupt Mode.
+     */
+    dmar_writeq(iommu->reg, DMAR_IRTA_REG,
+                ir_ctrl->iremap_maddr | IRTA_REG_TABLE_SIZE |
+                (eim ? IRTA_EIME : 0));
 
     /* set SIRTP */
     gcmd = dmar_readl(iommu->reg, DMAR_GSTS_REG);
diff --git a/xen/drivers/passthrough/vtd/qinval.c b/xen/drivers/passthrough/vtd/qinval.c
index e95dc54a8d..01447cf9a8 100644
--- a/xen/drivers/passthrough/vtd/qinval.c
+++ b/xen/drivers/passthrough/vtd/qinval.c
@@ -428,6 +428,8 @@ int enable_qinval(struct iommu *iommu)
     flush->context = flush_context_qi;
     flush->iotlb = flush_iotlb_qi;
 
+    spin_lock_irqsave(&iommu->register_lock, flags);
+
     /* Setup Invalidation Queue Address(IQA) register with the
      * address of the page we just allocated.  QS field at
      * bits[2:0] to indicate size of queue is one 4KB page.
@@ -435,10 +437,8 @@ int enable_qinval(struct iommu *iommu)
      * registers are automatically reset to 0 with write
      * to IQA register.
      */
-    qi_ctrl->qinval_maddr |= QINVAL_PAGE_ORDER;
-
-    spin_lock_irqsave(&iommu->register_lock, flags);
-    dmar_writeq(iommu->reg, DMAR_IQA_REG, qi_ctrl->qinval_maddr);
+    dmar_writeq(iommu->reg, DMAR_IQA_REG,
+                qi_ctrl->qinval_maddr | QINVAL_PAGE_ORDER);
 
     dmar_writeq(iommu->reg, DMAR_IQT_REG, 0);
 
diff --git a/xen/drivers/passthrough/vtd/utils.c b/xen/drivers/passthrough/vtd/utils.c
index 85e0f41d85..94a6e4eec9 100644
--- a/xen/drivers/passthrough/vtd/utils.c
+++ b/xen/drivers/passthrough/vtd/utils.c
@@ -204,8 +204,9 @@ void vtd_dump_iommu_info(unsigned char key)
         if ( status & DMA_GSTS_IRES )
         {
             /* Dump interrupt remapping table. */
-            u64 iremap_maddr = dmar_readq(iommu->reg, DMAR_IRTA_REG);
-            int nr_entry = 1 << ((iremap_maddr & 0xF) + 1);
+            uint64_t irta = dmar_readq(iommu->reg, DMAR_IRTA_REG);
+            uint64_t iremap_maddr = irta & PAGE_MASK;
+            unsigned int nr_entry = 1 << ((irta & 0xF) + 1);
             struct iremap_entry *iremap_entries = NULL;
             int print_cnt = 0;