diff --git a/ArmPkg/Include/Chipset/AArch64Mmu.h b/ArmPkg/Include/Chipset/AArch64Mmu.h
index 22e492d61d..3c3df6d983 100644
--- a/ArmPkg/Include/Chipset/AArch64Mmu.h
+++ b/ArmPkg/Include/Chipset/AArch64Mmu.h
@@ -74,6 +74,11 @@
 #define TT_NS                                   BIT5
 #define TT_AF                                   BIT10
 
+#define TT_SH_NON_SHAREABLE                     (0x0 << 8)
+#define TT_SH_OUTER_SHAREABLE                   (0x2 << 8)
+#define TT_SH_INNER_SHAREABLE                   (0x3 << 8)
+#define TT_SH_MASK                              (0x3 << 8)
+
 #define TT_PXN_MASK                             BIT53
 #define TT_UXN_MASK                             BIT54   // EL1&0
 #define TT_XN_MASK                              BIT54   // EL2 / EL3
diff --git a/ArmPkg/Include/Chipset/ArmV7Mmu.h b/ArmPkg/Include/Chipset/ArmV7Mmu.h
index 24ab1755fa..aaa0977205 100644
--- a/ArmPkg/Include/Chipset/ArmV7Mmu.h
+++ b/ArmPkg/Include/Chipset/ArmV7Mmu.h
@@ -175,14 +175,14 @@
 #define TT_DESCRIPTOR_SECTION_WRITE_BACK(NonSecure)         (TT_DESCRIPTOR_SECTION_TYPE_SECTION                                                           | \
                                                             ((NonSecure) ?  TT_DESCRIPTOR_SECTION_NS : 0)    | \
                                                             TT_DESCRIPTOR_SECTION_NG_GLOBAL                         | \
-                                                            TT_DESCRIPTOR_SECTION_S_NOT_SHARED                      | \
+                                                            TT_DESCRIPTOR_SECTION_S_SHARED                          | \
                                                             TT_DESCRIPTOR_SECTION_DOMAIN(0)                         | \
                                                             TT_DESCRIPTOR_SECTION_AP_RW_RW                          | \
                                                             TT_DESCRIPTOR_SECTION_CACHE_POLICY_WRITE_BACK_ALLOC)
 #define TT_DESCRIPTOR_SECTION_WRITE_THROUGH(NonSecure)      (TT_DESCRIPTOR_SECTION_TYPE_SECTION                                                           | \
                                                             ((NonSecure) ?  TT_DESCRIPTOR_SECTION_NS : 0)    | \
                                                             TT_DESCRIPTOR_SECTION_NG_GLOBAL                         | \
-                                                            TT_DESCRIPTOR_SECTION_S_NOT_SHARED                      | \
+                                                            TT_DESCRIPTOR_SECTION_S_SHARED                          | \
                                                             TT_DESCRIPTOR_SECTION_DOMAIN(0)                         | \
                                                             TT_DESCRIPTOR_SECTION_AP_RW_RW                          | \
                                                             TT_DESCRIPTOR_SECTION_CACHE_POLICY_WRITE_THROUGH_NO_ALLOC)
@@ -203,12 +203,12 @@
 
 #define TT_DESCRIPTOR_PAGE_WRITE_BACK              (TT_DESCRIPTOR_PAGE_TYPE_PAGE                                                           | \
                                                         TT_DESCRIPTOR_PAGE_NG_GLOBAL                                                      | \
-                                                        TT_DESCRIPTOR_PAGE_S_NOT_SHARED                                                   | \
+                                                        TT_DESCRIPTOR_PAGE_S_SHARED                                                       | \
                                                         TT_DESCRIPTOR_PAGE_AP_RW_RW                                                       | \
                                                         TT_DESCRIPTOR_PAGE_CACHE_POLICY_WRITE_BACK_ALLOC)
 #define TT_DESCRIPTOR_PAGE_WRITE_THROUGH           (TT_DESCRIPTOR_PAGE_TYPE_PAGE                                                           | \
                                                         TT_DESCRIPTOR_PAGE_NG_GLOBAL                                                      | \
-                                                        TT_DESCRIPTOR_PAGE_S_NOT_SHARED                                                   | \
+                                                        TT_DESCRIPTOR_PAGE_S_SHARED                                                       | \
                                                         TT_DESCRIPTOR_PAGE_AP_RW_RW                                                       | \
                                                         TT_DESCRIPTOR_PAGE_CACHE_POLICY_WRITE_THROUGH_NO_ALLOC)
 #define TT_DESCRIPTOR_PAGE_DEVICE                  (TT_DESCRIPTOR_PAGE_TYPE_PAGE                                                           | \
diff --git a/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c b/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
index e40c09ae96..8829c6286b 100644
--- a/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
+++ b/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
@@ -34,23 +34,22 @@ ArmMemoryAttributeToPageAttribute (
 {
   switch (Attributes) {
   case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK:
-    return TT_ATTR_INDX_MEMORY_WRITE_BACK;
-  case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH:
-    return TT_ATTR_INDX_MEMORY_WRITE_THROUGH;
-  case ARM_MEMORY_REGION_ATTRIBUTE_DEVICE:
-    return TT_ATTR_INDX_DEVICE_MEMORY;
-  case ARM_MEMORY_REGION_ATTRIBUTE_UNCACHED_UNBUFFERED:
-    return TT_ATTR_INDX_MEMORY_NON_CACHEABLE;
   case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK:
-    return TT_ATTR_INDX_MEMORY_WRITE_BACK;
+    return TT_ATTR_INDX_MEMORY_WRITE_BACK | TT_SH_INNER_SHAREABLE;
+
+  case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH:
   case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_THROUGH:
-    return TT_ATTR_INDX_MEMORY_WRITE_THROUGH;
-  case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_DEVICE:
-    return TT_ATTR_INDX_DEVICE_MEMORY;
+    return TT_ATTR_INDX_MEMORY_WRITE_THROUGH | TT_SH_INNER_SHAREABLE;
+
+  // Uncached and device mappings are treated as outer shareable by default,
+  case ARM_MEMORY_REGION_ATTRIBUTE_UNCACHED_UNBUFFERED:
   case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_UNCACHED_UNBUFFERED:
     return TT_ATTR_INDX_MEMORY_NON_CACHEABLE;
+
   default:
     ASSERT(0);
+  case ARM_MEMORY_REGION_ATTRIBUTE_DEVICE:
+  case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_DEVICE:
     return TT_ATTR_INDX_DEVICE_MEMORY;
   }
 }