---
 include/linux/ipipe_base.h  |    6 ++++
 include/linux/ipipe_trace.h |    7 ++++-
 include/linux/kernel.h      |    8 ++++-
 include/linux/preempt.h     |   59 +++++++++++++++++---------------------------
 include/linux/smp.h         |   14 ++++++++--
 kernel/ipipe/Kconfig.debug  |    9 ++++++
 kernel/ipipe/core.c         |   25 ++++++++++++++++++
 7 files changed, 88 insertions(+), 40 deletions(-)

Index: linux-2.6.20/include/linux/ipipe_base.h
===================================================================
--- linux-2.6.20.orig/include/linux/ipipe_base.h
+++ linux-2.6.20/include/linux/ipipe_base.h
@@ -75,6 +75,12 @@ void __ipipe_unstall_root(void);
 
 void __ipipe_restore_root(unsigned long x);
 
+#ifdef CONFIG_IPIPE_DEBUG_CONTEXT
+void ipipe_check_context(struct ipipe_domain *border_ipd);
+#else /* !CONFIG_IPIPE_DEBUG_CONTEXT */
+static inline void ipipe_check_context(struct ipipe_domain *border_ipd) { }
+#endif /* !CONFIG_IPIPE_DEBUG_CONTEXT */
+
 #endif	/* CONFIG_IPIPE */
 
 #endif	/* !__LINUX_IPIPE_BASE_H */
Index: linux-2.6.20/include/linux/kernel.h
===================================================================
--- linux-2.6.20.orig/include/linux/kernel.h
+++ linux-2.6.20/include/linux/kernel.h
@@ -14,6 +14,7 @@
 #include <linux/compiler.h>
 #include <linux/bitops.h>
 #include <linux/log2.h>
+#include <linux/ipipe_base.h>
 #include <asm/byteorder.h>
 #include <asm/bug.h>
 
@@ -72,9 +73,12 @@ struct user;
  */
 #ifdef CONFIG_PREEMPT_VOLUNTARY
 extern int cond_resched(void);
-# define might_resched() cond_resched()
+# define might_resched() do { \
+		ipipe_check_context(ipipe_root_domain); \
+		cond_resched(); \
+	} while (0)
 #else
-# define might_resched() do { } while (0)
+# define might_resched() ipipe_check_context(ipipe_root_domain)
 #endif
 
 #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
Index: linux-2.6.20/include/linux/preempt.h
===================================================================
--- linux-2.6.20.orig/include/linux/preempt.h
+++ linux-2.6.20/include/linux/preempt.h
@@ -8,6 +8,7 @@
 
 #include <linux/thread_info.h>
 #include <linux/linkage.h>
+#include <linux/ipipe_base.h>
 
 #ifdef CONFIG_DEBUG_PREEMPT
   extern void fastcall add_preempt_count(int val);
@@ -26,52 +27,40 @@
 
 asmlinkage void preempt_schedule(void);
 
-#ifdef CONFIG_IPIPE
-#include <asm/ipipe.h>
-DECLARE_PER_CPU(struct ipipe_domain *, ipipe_percpu_domain);
-extern struct ipipe_domain ipipe_root;
-#define ipipe_preempt_guard() (per_cpu(ipipe_percpu_domain, ipipe_processor_id()) == &ipipe_root)
-#else  /* !CONFIG_IPIPE */
-#define ipipe_preempt_guard()	1
-#endif /* CONFIG_IPIPE */
-
-#define preempt_disable()						\
-do {									\
-	if (ipipe_preempt_guard()) {					\
-		inc_preempt_count();					\
-		barrier();						\
-	}								\
+#define preempt_disable() \
+do { \
+	ipipe_check_context(ipipe_root_domain); \
+	inc_preempt_count(); \
+	barrier(); \
 } while (0)
 
-#define preempt_enable_no_resched()					\
-do {									\
-	if (ipipe_preempt_guard()) {					\
-		barrier();						\
-		dec_preempt_count();					\
-	}								\
+#define preempt_enable_no_resched() \
+do { \
+	ipipe_check_context(ipipe_root_domain); \
+	barrier(); \
+	dec_preempt_count(); \
 } while (0)
 
-#define preempt_check_resched()						\
-do {									\
-	if (ipipe_preempt_guard()) {					\
-		if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))	\
-			preempt_schedule();				\
-	}								\
+#define preempt_check_resched() \
+do { \
+	ipipe_check_context(ipipe_root_domain); \
+	if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
+		preempt_schedule(); \
 } while (0)
 
-#define preempt_enable()						\
-do {									\
-	preempt_enable_no_resched();					\
+#define preempt_enable() \
+do { \
+	preempt_enable_no_resched(); \
 	barrier(); \
-	preempt_check_resched();					\
+	preempt_check_resched(); \
 } while (0)
 
 #else
 
-#define preempt_disable()		do { } while (0)
-#define preempt_enable_no_resched()	do { } while (0)
-#define preempt_enable()		do { } while (0)
-#define preempt_check_resched()		do { } while (0)
+#define preempt_disable()		ipipe_check_context(ipipe_root_domain)
+#define preempt_enable_no_resched()	ipipe_check_context(ipipe_root_domain)
+#define preempt_enable()		ipipe_check_context(ipipe_root_domain)
+#define preempt_check_resched()		ipipe_check_context(ipipe_root_domain)
 
 #endif
 
Index: linux-2.6.20/kernel/ipipe/Kconfig.debug
===================================================================
--- linux-2.6.20.orig/kernel/ipipe/Kconfig.debug
+++ linux-2.6.20/kernel/ipipe/Kconfig.debug
@@ -2,6 +2,15 @@ config IPIPE_DEBUG
 	bool "I-pipe debugging"
 	depends on IPIPE
 
+config IPIPE_DEBUG_CONTEXT
+	bool "Check for illicit cross-domain calls"
+	depends on IPIPE_DEBUG
+	---help---
+	  Enable this feature to arm checkpoints in the kernel that
+	  verify the correct invocation context. On entry of critical
+	  Linux services a warning is issued if the caller is not
+	  running over the root domain.
+
 config IPIPE_TRACE
 	bool "Latency tracing"
 	depends on IPIPE_DEBUG
Index: linux-2.6.20/kernel/ipipe/core.c
===================================================================
--- linux-2.6.20.orig/kernel/ipipe/core.c
+++ linux-2.6.20/kernel/ipipe/core.c
@@ -33,6 +33,7 @@
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #endif	/* CONFIG_PROC_FS */
+#include <linux/ipipe_trace.h>
 
 static int __ipipe_ptd_key_count;
 
@@ -1383,6 +1384,30 @@ void __init ipipe_init_proc(void)
 
 #endif	/* CONFIG_PROC_FS */
 
+#ifdef CONFIG_IPIPE_DEBUG_CONTEXT
+void ipipe_check_context(struct ipipe_domain *border_ipd)
+{
+	static int check_hit;
+
+	if (likely(ipipe_current_domain->priority <= border_ipd->priority) ||
+	    check_hit)
+		return;
+
+	check_hit = 1;
+
+	ipipe_trace_panic_freeze();
+	ipipe_set_printk_sync(ipipe_current_domain);
+	printk(KERN_ERR "I-pipe: Detected illicit call from domain '%s'\n"
+	       KERN_ERR "        into a service reserved for domain '%s' and "
+			"below.\n",
+	       ipipe_current_domain->name, border_ipd->name);
+	show_stack(NULL, NULL);
+	ipipe_trace_panic_dump();
+}
+
+EXPORT_SYMBOL(ipipe_check_context);
+#endif /* CONFIG_IPIPE_DEBUG_CONTEXT */
+
 EXPORT_SYMBOL(ipipe_virtualize_irq);
 EXPORT_SYMBOL(ipipe_control_irq);
 EXPORT_SYMBOL(ipipe_suspend_domain);
Index: linux-2.6.20/include/linux/smp.h
===================================================================
--- linux-2.6.20.orig/include/linux/smp.h
+++ linux-2.6.20/include/linux/smp.h
@@ -109,6 +109,8 @@ static inline int smp_call_function_sing
 
 #endif /* !SMP */
 
+#include <linux/ipipe_base.h>
+
 /*
  * smp_processor_id(): get the current CPU ID.
  *
@@ -126,9 +128,17 @@ static inline int smp_call_function_sing
  */
 #ifdef CONFIG_DEBUG_PREEMPT
   extern unsigned int debug_smp_processor_id(void);
-# define smp_processor_id() debug_smp_processor_id()
+# define smp_processor_id()				\
+	({						\
+		ipipe_check_context(ipipe_root_domain);	\
+		debug_smp_processor_id();		\
+	})
 #else
-# define smp_processor_id() raw_smp_processor_id()
+# define smp_processor_id()				\
+	({						\
+		ipipe_check_context(ipipe_root_domain);	\
+		raw_smp_processor_id();			\
+	})
 #endif
 
 #define get_cpu()		({ preempt_disable(); smp_processor_id(); })
Index: linux-2.6.20/include/linux/ipipe_trace.h
===================================================================
--- linux-2.6.20.orig/include/linux/ipipe_trace.h
+++ linux-2.6.20/include/linux/ipipe_trace.h
@@ -39,6 +39,11 @@ int ipipe_trace_frozen_reset(void);
 void ipipe_trace_panic_freeze(void);
 void ipipe_trace_panic_dump(void);
 
-#endif /* CONFIG_IPIPE_TRACE */
+#else /* !CONFIG_IPIPE_TRACE */
+
+static inline void ipipe_trace_panic_freeze(void) { }
+static inline void ipipe_trace_panic_dump(void) { }
+
+#endif /* !CONFIG_IPIPE_TRACE */
 
 #endif	/* !__LINUX_IPIPE_H */