diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index f8da4fe0e7..76025f6ccd 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -245,11 +245,11 @@ static u64 bus_to_context_maddr(struct vtd_iommu *iommu, u8 bus)
             unmap_vtd_domain_page(root_entries);
             return 0;
         }
-        set_root_value(*root, maddr);
+        set_root_ctp(*root, maddr);
         set_root_present(*root);
         iommu_sync_cache(root, sizeof(struct root_entry));
     }
-    maddr = (u64) get_context_addr(*root);
+    maddr = root_ctp(*root);
     unmap_vtd_domain_page(root_entries);
     return maddr;
 }
diff --git a/xen/drivers/passthrough/vtd/iommu.h b/xen/drivers/passthrough/vtd/iommu.h
index 216791b3d6..031ac5f66c 100644
--- a/xen/drivers/passthrough/vtd/iommu.h
+++ b/xen/drivers/passthrough/vtd/iommu.h
@@ -184,21 +184,28 @@
 #define dma_frcd_source_id(c) (c & 0xffff)
 #define dma_frcd_page_addr(d) (d & (((u64)-1) << 12)) /* low 64 bit */
 
-/*
- * 0: Present
- * 1-11: Reserved
- * 12-63: Context Ptr (12 - (haw-1))
- * 64-127: Reserved
- */
 struct root_entry {
-    u64    val;
-    u64    rsvd1;
+    union {
+        __uint128_t val;
+        struct { uint64_t lo, hi; };
+        struct {
+            /* 0 - 63 */
+            uint64_t p:1;
+            uint64_t reserved0:11;
+            uint64_t ctp:52;
+
+            /* 64 - 127 */
+            uint64_t reserved1;
+        };
+    };
 };
-#define root_present(root)    ((root).val & 1)
-#define set_root_present(root) do {(root).val |= 1;} while(0)
-#define get_context_addr(root) ((root).val & PAGE_MASK_4K)
-#define set_root_value(root, value) \
-    do {(root).val |= ((value) & PAGE_MASK_4K);} while(0)
+
+#define root_present(r) (r).p
+#define set_root_present(r) do { (r).p = 1; } while (0)
+
+#define root_ctp(r) ((r).ctp << PAGE_SHIFT_4K)
+#define set_root_ctp(r, val) \
+    do { (r).ctp = ((val) >> PAGE_SHIFT_4K); } while (0)
 
 struct context_entry {
     u64 lo;
diff --git a/xen/drivers/passthrough/vtd/utils.c b/xen/drivers/passthrough/vtd/utils.c
index 4febcf506d..4c85242894 100644
--- a/xen/drivers/passthrough/vtd/utils.c
+++ b/xen/drivers/passthrough/vtd/utils.c
@@ -112,7 +112,7 @@ void print_vtd_entries(struct vtd_iommu *iommu, int bus, int devfn, u64 gmfn)
         return;
     }
 
-    printk("    root_entry[%02x] = %"PRIx64"\n", bus, root_entry[bus].val);
+    printk("    root_entry[%02x] = %"PRIx64"\n", bus, root_entry[bus].lo);
     if ( !root_present(root_entry[bus]) )
     {
         unmap_vtd_domain_page(root_entry);
@@ -120,7 +120,7 @@ void print_vtd_entries(struct vtd_iommu *iommu, int bus, int devfn, u64 gmfn)
         return;
     }
 
-    val = root_entry[bus].val;
+    val = root_ctp(root_entry[bus]);
     unmap_vtd_domain_page(root_entry);
     ctxt_entry = map_vtd_domain_page(val);
     if ( ctxt_entry == NULL )
diff --git a/xen/drivers/passthrough/vtd/x86/ats.c b/xen/drivers/passthrough/vtd/x86/ats.c
index 04d702b1d6..8369415dcc 100644
--- a/xen/drivers/passthrough/vtd/x86/ats.c
+++ b/xen/drivers/passthrough/vtd/x86/ats.c
@@ -74,8 +74,8 @@ int ats_device(const struct pci_dev *pdev, const struct acpi_drhd_unit *drhd)
 static bool device_in_domain(const struct vtd_iommu *iommu,
                              const struct pci_dev *pdev, uint16_t did)
 {
-    struct root_entry *root_entry;
-    struct context_entry *ctxt_entry = NULL;
+    struct root_entry *root_entry, *root_entries = NULL;
+    struct context_entry *context_entry, *context_entries = NULL;
     unsigned int tt;
     bool found = false;
 
@@ -85,25 +85,28 @@ static bool device_in_domain(const struct vtd_iommu *iommu,
         return false;
     }
 
-    root_entry = map_vtd_domain_page(iommu->root_maddr);
-    if ( !root_present(root_entry[pdev->bus]) )
+    root_entries = (struct root_entry *)map_vtd_domain_page(iommu->root_maddr);
+    root_entry = &root_entries[pdev->bus];
+    if ( !root_present(*root_entry) )
         goto out;
 
-    ctxt_entry = map_vtd_domain_page(root_entry[pdev->bus].val);
-    if ( context_domain_id(ctxt_entry[pdev->devfn]) != did )
+    context_entries = map_vtd_domain_page(root_ctp(*root_entry));
+    context_entry = &context_entries[pdev->devfn];
+    if ( context_domain_id(*context_entry) != did )
         goto out;
 
-    tt = context_translation_type(ctxt_entry[pdev->devfn]);
+    tt = context_translation_type(*context_entry);
     if ( tt != CONTEXT_TT_DEV_IOTLB )
         goto out;
 
     found = true;
-out:
-    if ( root_entry )
-        unmap_vtd_domain_page(root_entry);
 
-    if ( ctxt_entry )
-        unmap_vtd_domain_page(ctxt_entry);
+ out:
+    if ( root_entries )
+        unmap_vtd_domain_page(root_entries);
+
+    if ( context_entries )
+        unmap_vtd_domain_page(context_entries);
 
     return found;
 }
