arm64/ipipe: use fast domain check in exception path

arch/arm64/kernel/asm-offsets.c

@@ -34,6 +34,9 @@ int main(void)
   DEFINE(TSK_ACTIVE_MM,		offsetof(struct task_struct, active_mm));
   BLANK();
   DEFINE(TI_FLAGS,		offsetof(struct thread_info, flags));
+#ifdef CONFIG_IPIPE
+  DEFINE(TI_IPIPE,		offsetof(struct thread_info, ipipe_flags));
+#endif
   DEFINE(TI_PREEMPT,		offsetof(struct thread_info, preempt_count));
   DEFINE(TI_ADDR_LIMIT,		offsetof(struct thread_info, addr_limit));
   DEFINE(TI_TASK,		offsetof(struct thread_info, task));

arch/arm64/kernel/entry.S

@@ -607,17 +607,6 @@ el0_irq_naked:
 	b	ret_to_user
 ENDPROC(el0_irq)
 
-#ifdef CONFIG_IPIPE
-ret_from_exception:
-	disable_irq
-	bl	__ipipe_check_root
-	cmp     x0, #1
-	bne	__ipipe_ret_to_user_irqs_disabled  //Fast exit path over non-root domains
-	ct_user_exit
-	b	ret_to_user
-ENDPROC(ret_from_exception)
-#endif
-
 /*
  * Register switch for AArch64. The callee-saved registers need to be saved
  * and restored. On entry:
@@ -661,14 +650,16 @@ ret_fast_syscall:
 	kernel_exit 0, ret = 1
 
 #ifdef CONFIG_IPIPE
+ret_from_exception:
+	ldr	x0, [tsk, #TI_IPIPE]
+	tst	x0, #_TIP_HEAD
+	b.eq	ret_to_user
 __ipipe_ret_to_user:
-	disable_irq				// disable interrupts
-ENTRY(__ipipe_ret_to_user_irqs_disabled)
+	disable_irq
+__ipipe_ret_to_user_irqs_disabled:
 	kernel_exit 0, ret = 0
-ENDPROC(__ipipe_ret_to_user_irqs_disabled)
 #endif /* CONFIG_IPIPE */
 
-
 /*
  * Ok, we need to do extra processing, enter the slow path.
  */

arch/arm64/kernel/ipipe.c

@@ -305,11 +305,6 @@ unsigned asmlinkage __ipipe_bugon_irqs_enabled(unsigned x)
 }
 #endif
 
-asmlinkage int __ipipe_check_root(void)
-{
-	return __ipipe_root_p;
-}
-
 asmlinkage int __ipipe_check_root_interruptible(void)
 {
 	return __ipipe_root_p && !irqs_disabled();