diff --git a/include/aos/threads.h b/include/aos/threads.h
index f615146..4e6d2c9 100644
--- a/include/aos/threads.h
+++ b/include/aos/threads.h
@@ -122,6 +122,8 @@ static inline void thread_once(thread_once_t *control, void (*func)(void)) {
  */
 void thread_set_status(int status);
 
+void thread_allocate_stack(struct thread *thread);
+
 __END_DECLS
 
 #endif  // LIBBARRELFISH_THREADS_H
diff --git a/lib/aos/threads.c b/lib/aos/threads.c
index d730fab..7845b4b 100644
--- a/lib/aos/threads.c
+++ b/lib/aos/threads.c
@@ -347,9 +347,8 @@ struct thread *thread_create_unrunnable(thread_func_t start_func, void *arg,
     // allocate stack
     // debug_printf("[thread_create_unrunnable] stacksize = %x\n", stacksize);
     assert((stacksize % sizeof(uintptr_t)) == 0);
-    stacksize += BASE_PAGE_SIZE;
     size_t bytes_allocated;
-    void *stack = paging_malloc(stacksize, &bytes_allocated, BASE_PAGE_SIZE);
+    void *stack = paging_malloc(stacksize + BASE_PAGE_SIZE, &bytes_allocated, BASE_PAGE_SIZE) + BASE_PAGE_SIZE;
     if (stack == NULL) {
         return NULL;
     }
@@ -362,7 +361,7 @@ struct thread *thread_create_unrunnable(thread_func_t start_func, void *arg,
     release_spinlock(&thread_slabs_spinlock);
     // thread_mutex_unlock(&thread_slabs_mutex);
     if (space == NULL) {
-        free(stack);
+        // free(stack);
         return NULL;
     }
 
@@ -1463,3 +1462,13 @@ void thread_deliver_exception_disabled(dispatcher_handle_t handle,
 
     disp_resume(handle, &thread->regs);
 }
+
+/**
+ * \brief Allocate all pages of the thread stack.
+ */
+void thread_allocate_stack(struct thread *thread)
+{
+    for (volatile uint8_t *p = thread->stack; (void*)p < thread->stack_top; p += BASE_PAGE_SIZE) {
+        *p; // cause a page fault
+    }
+}
diff --git a/usr/init/main.c b/usr/init/main.c
index ee825c0..72f37ed 100644
--- a/usr/init/main.c
+++ b/usr/init/main.c
@@ -230,8 +230,6 @@ app_main(int argc, char *argv[]) {
     // - grading_test_early();
     // - grading_test_late();
 
-    // Grading
-    grading_setup_app_init(bi);
 
     // TODO: initialize mem allocator, vspace management here
     err = cap_retype(cap_selfep, cap_dispatcher, 0, ObjType_EndPointLMP, 0, 1);
@@ -248,22 +246,36 @@ app_main(int argc, char *argv[]) {
 
     ram_alloc_set(ram_alloc_remote_core);
 
-    thread_create(urpc_server, &urpc_to_app_server);
+    struct thread *urpc_server_thread = thread_create(urpc_server, &urpc_to_app_server);
+    // Allocate all pages of the thread stack now.
+    // We can't have page fault while the thread is running,
+    // because URPC calls may only be done from the main thread.
+    thread_allocate_stack(urpc_server_thread);
 
-    // Grading
-    grading_test_early();
 
     // TODO: Spawn system processes etc. here
 
     struct bootinfo_serialized * bi_ser;
     err = aos_urpc_get_bootinfo(&urpc_to_bsp, &bi_ser);
-    if (err_is_fail(err)) return err;
+    if (err_is_fail(err)) {
+        DEBUG_ERR(err, "in aos_urpc_get_bootinfo");
+        abort();
+    }
     err = deserialize_bootinfo(bi_ser, &bi);
+    if (err_is_fail(err)) {
+        DEBUG_ERR(err, "in deserialize_bootinfo");
+        abort();
+    }
     free(bi_ser);
-    if (err_is_fail(err)) return err;
 
     debug_printf("[app_main]: received bootinfo with %d regions\n", bi->regions_length);
 
+    // Grading
+    grading_setup_app_init(bi);
+
+    // Grading
+    grading_test_early();
+
     // Grading
     grading_test_late();