New UTCB implementation almost working.

- KIP's pointer to UTCB seems to work with existing l4lib ipc functions.
- Works up to clone()
- In clone we mmap() the same UTCB on each new thread - excessive.
- Generally during page fault handling, cloned threads may fault on the same page
  multiple times even though a single handling would be enough for all of them.
  Need to detect and handle this.

src/generic/scheduler.c

@@ -255,12 +255,12 @@ static inline void context_switch(struct ktcb *next)
 
 	// printk("(%d) to (%d)\n", cur->tid, next->tid);
 
-	/* Update KIP UTCB pointer for new thread to run */
-	kip.utcb = next->utcb_address;
-
 	/* Flush caches and everything */
 	arch_hardware_flush(next->pgd);
 
+	/* Update utcb region for next task */
+	task_update_utcb(cur, next);
+
 	/* Switch context */
 	arch_switch(cur, next);
 

src/generic/tcb.c

@@ -8,7 +8,10 @@
 #include <l4/generic/scheduler.h>
 #include <l4/generic/preempt.h>
 #include <l4/lib/idpool.h>
+#include <l4/api/kip.h>
 #include INC_ARCH(exception.h)
+#include INC_SUBARCH(mm.h)
+#include INC_GLUE(memory.h)
 
 /* ID pools for threads and spaces. */
 struct id_pool *thread_id_pool;
@@ -22,3 +25,36 @@ struct list_head global_task_list;
 unsigned int need_resched_offset = offsetof(struct ktcb, ts_need_resched);
 unsigned int syscall_regs_offset = offsetof(struct ktcb, syscall_regs);
 
+/*
+ * Every thread has a unique utcb region that is mapped to its address
+ * space as its context is loaded. The utcb region is a function of
+ * this mapping and its offset that is reached via the KIP UTCB pointer
+ */
+void task_update_utcb(struct ktcb *cur, struct ktcb *next)
+{
+	/* Update the KIP pointer */
+	kip.utcb = next->utcb_address;
+
+	/* We stick with KIP update and no private tls mapping for now */
+#if 0
+	/*
+	 * Unless current and next are in the same address
+	 * space and sharing the same physical utcb page, we
+	 * update the mapping
+	 */
+	if (cur->utcb_phys != next->utcb_phys)
+		add_mapping(page_align(next->utcb_phys),
+			    page_align(next->utcb_virt),
+			    page_align_up(UTCB_SIZE),
+			    MAP_USR_RW_FLAGS);
+	/*
+	 * If same physical utcb but different pgd, it means two
+	 * address spaces share the same utcb. We treat this as a
+	 * bug for now.
+	 */
+	else
+		BUG_ON(cur->pgd != next->pgd);
+#endif
+
+}
+