diff --git a/init/builtins.cpp b/init/builtins.cpp
index 538ed00..6511d29 100644
--- a/init/builtins.cpp
+++ b/init/builtins.cpp
@@ -1119,13 +1119,21 @@
 }
 
 static Result<Success> do_setup_runtime_bionic(const BuiltinArguments& args) {
-    if (SwitchToDefaultMountNamespace()) {
+    if (SetupRuntimeBionic()) {
         return Success();
     } else {
         return Error() << "Failed to setup runtime bionic";
     }
 }
 
+static Result<Success> do_enter_default_mount_ns(const BuiltinArguments& args) {
+    if (SwitchToDefaultMountNamespace()) {
+        return Success();
+    } else {
+        return Error() << "Failed to enter into default mount namespace";
+    }
+}
+
 // Builtin-function-map start
 const BuiltinFunctionMap::Map& BuiltinFunctionMap::map() const {
     constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
@@ -1177,6 +1185,7 @@
         {"start",                   {1,     1,    {false,  do_start}}},
         {"stop",                    {1,     1,    {false,  do_stop}}},
         {"swapon_all",              {1,     1,    {false,  do_swapon_all}}},
+        {"enter_default_mount_ns",  {0,     0,    {false,  do_enter_default_mount_ns}}},
         {"symlink",                 {2,     2,    {true,   do_symlink}}},
         {"sysclktz",                {1,     1,    {false,  do_sysclktz}}},
         {"trigger",                 {1,     1,    {false,  do_trigger}}},
diff --git a/init/mount_namespace.cpp b/init/mount_namespace.cpp
index 413fe8f..327446a 100644
--- a/init/mount_namespace.cpp
+++ b/init/mount_namespace.cpp
@@ -172,6 +172,11 @@
                          kBionicLibsMountPointDir64))
         return false;
 
+    // /apex is also a private mountpoint to give different sets of APEXes for
+    // the bootstrap and default mount namespaces. The processes running with
+    // the bootstrap namespace get APEXes from the read-only partition.
+    if (!(MakePrivate("/apex"))) return false;
+
     bootstrap_ns_fd.reset(OpenMountNamespace());
     bootstrap_ns_id = GetMountNamespaceId();
 
@@ -227,6 +232,17 @@
         }
     }
 
+    LOG(INFO) << "Switched to default mount namespace";
+    return true;
+}
+
+// TODO(jiyong): remove this when /system/lib/libc.so becomes
+// a symlink to /apex/com.android.runtime/lib/bionic/libc.so
+bool SetupRuntimeBionic() {
+    if (IsRecoveryMode()) {
+        // We don't have multiple namespaces in recovery mode
+        return true;
+    }
     // Bind-mount bionic from the runtime APEX since it is now available. Note
     // that in case of IsBionicUpdatable() == false, these mounts are over the
     // existing existing bind mounts for the bootstrap bionic, which effectively
@@ -238,7 +254,7 @@
                          kBionicLibsMountPointDir64))
         return false;
 
-    LOG(INFO) << "Switched to default mount namespace";
+    LOG(INFO) << "Runtime bionic is set up";
     return true;
 }
 
diff --git a/init/mount_namespace.h b/init/mount_namespace.h
index c41a449..4eef785 100644
--- a/init/mount_namespace.h
+++ b/init/mount_namespace.h
@@ -20,6 +20,7 @@
 namespace init {
 
 bool SetupMountNamespaces();
+bool SetupRuntimeBionic();
 bool SwitchToDefaultMountNamespace();
 bool SwitchToBootstrapMountNamespaceIfNeeded();