Removed bits from kernel where pager utcb is set.

Pagers now set their own utcb explicitly via exchange_registers.
exregs accepts calls from active pagers for this purpose only.

src/api/syscall.c

@@ -10,6 +10,8 @@
 #include <l4/generic/resource.h>
 #include <l4/generic/tcb.h>
 #include <l4/generic/space.h>
+#include <l4/generic/capability.h>
+#include <l4/generic/container.h>
 #include <l4/api/space.h>
 #include <l4/api/ipc.h>
 #include <l4/api/kip.h>
@@ -33,6 +35,8 @@ void do_exchange_registers(struct ktcb *task, struct exregs_data *exregs)
 {
 	task_context_t *context = &task->context;
 
+	if (!exregs->valid_vect)
+		goto flags;
 	/*
 	 * NOTE:
 	 * We don't care if register values point at invalid addresses
@@ -74,29 +78,48 @@ void do_exchange_registers(struct ktcb *task, struct exregs_data *exregs)
 	if (exregs->valid_vect & FIELD_TO_BIT(exregs_context_t, pc))
 		context->pc = exregs->context.pc;
 
+flags:
 	/* Set thread's pager if one is supplied */
 	if (exregs->flags & EXREGS_SET_PAGER)
 		task->pagerid = exregs->pagerid;
 
 	/* Set thread's utcb if supplied */
-	if (exregs->flags & EXREGS_SET_UTCB)
+	if (exregs->flags & EXREGS_SET_UTCB) {
 		task->utcb_address = exregs->utcb_address;
+
+		/*
+		 * If task is the one currently runnable,
+		 * update kip utcb reference
+		 */
+		if (task == current)
+			task_update_utcb(task);
+	}
 }
 
 /*
  * exchange_registers()
  *
  * This call is used by the pagers to set (and in the future read)
- * the register context of a thread. The thread's registers can be
- * set only when the thread is in user mode. A newly created thread
- * that is the copy of another thread (forked or cloned) will also
- * be given its user mode context on the first chance to execute so
- * such threads can also be modified by this call before execution.
+ * the register context of a thread. The thread's registers that are
+ * set by this call are loaded whenever the thread gets a chance to
+ * run in user mode.
+ *
+ * It is ensured that whenever this call is made, the thread is
+ * either already running in user mode, or has been suspended in
+ * kernel mode, just before returning to user mode.
+ *
+ * A newly created thread that is the copy of another thread (forked
+ * or cloned) will also be given its user mode context on the first
+ * chance to execute so such threads can also be modified by this
+ * call before execution.
  *
  * A thread executing in the kernel cannot be modified since this
  * would compromise the kernel. Also the thread must be in suspended
  * condition so that the scheduler does not execute it as we modify
  * its context.
+ *
+ * FIXME: Still looks like suspended threads in the kernel
+ * need to be made immutable. see src/glue/arm/systable.c
  */
 int sys_exchange_registers(struct exregs_data *exregs, l4id_t tid)
 {
@@ -114,30 +137,27 @@ int sys_exchange_registers(struct exregs_data *exregs, l4id_t tid)
 	if (!mutex_trylock(&task->thread_control_lock))
 		return -EAGAIN;
 
-	/* Now check that the task is suspended */
-	if (task->state != TASK_INACTIVE) {
+	/*
+	 * Now check that the task is suspended.
+	 *
+	 * Only modification of non-register fields are
+	 * allowed on active tasks and those tasks must
+	 * be the pagers making the call on themselves.
+	 */
+	if (task->state != TASK_INACTIVE && exregs->valid_vect &&
+	    current != task && task->pager->tcb != current) {
 		err = -EACTIVE;
 		goto out;
 	}
 
-#if 0
-	A suspended thread implies it cannot do any harm
-	even if it is in kernel mode.
 	/*
-	 * The thread must be in user mode for its context
-	 * to be modified.
+	 * FIXME:
+	 * Capability Check.
+	 * Whose clist are we ought to check? Pager's or threads?
+	 * Need to check exregs capability
+	 * Need to check utcb capability if present.
+	 * if ((exregs->flags & EXREGS_SET_UTCB) &&
 	 */
-	if (!TASK_IN_USER(task)) {
-		err = -EPERM;
-		goto out;
-	}
-#endif
-
-	/* Check UTCB is in valid range */
-	if (exregs->flags & EXREGS_SET_UTCB &&
-	    !(exregs->utcb_address >= UTCB_AREA_START &&
-	    exregs->utcb_address < UTCB_AREA_END))
-		return -EINVAL;
 
 	/* Copy registers */
 	do_exchange_registers(task, exregs);

src/generic/capability.c

@@ -61,10 +61,8 @@ struct capability *capability_find_by_rtype(struct cap_list *clist,
 {
 	struct capability *cap;
 
-	list_foreach_struct(cap, &clist->caps, list) {
+	list_foreach_struct(cap, &clist->caps, list)
 		if ((cap->type & CAP_RTYPE_MASK) == rtype)
 			return cap;
-	}
 	return 0;
 }
-

src/generic/container.c

@@ -23,7 +23,7 @@ int container_init(struct container *c)
 	init_ktcb_list(&c->ktcb_list);
 	init_mutex_queue_head(&c->mutex_queue_head);
 
-	/* Ini pager structs */
+	/* Init pager structs */
 	for (int i = 0; i < CONFIG_MAX_PAGERS_USED; i++)
 		cap_list_init(&c->pager[i].cap_list);
 
@@ -48,23 +48,23 @@ void kcont_insert_container(struct container *c,
 }
 
 /*
+ * FIXME: Remove completely. Need to be done in userspace.
  * This searches pager capabilities and if it has a virtual memory area
  * defined as a UTCB, uses the first entry as its utcb. If not, it is
  * not an error, perhaps another pager will map its utcb.
  */
-void task_setup_utcb(struct ktcb *task, struct pager *pager)
+void pager_init_utcb(struct ktcb *task, struct pager *pager)
 {
 	struct capability *cap;
 
 	/* Find a virtual memory capability with UTCB map permissions */
 	list_foreach_struct(cap, &pager->cap_list.caps, list) {
-		if (((cap->type & CAP_RTYPE_MASK) ==
-		     CAP_RTYPE_VIRTMEM) &&
-		    (cap->access & CAP_MAP_UTCB)) {
-			/* Use first address slot as pager's utcb */
-			task->utcb_address = __pfn_to_addr(cap->start);
-			return;
-		}
+		if (cap_rtype(cap) == CAP_RTYPE_VIRTMEM &&
+		    cap->access & CAP_MAP_UTCB) {
+ 			/* Use first address slot as pager's utcb */
+ 			task->utcb_address = __pfn_to_addr(cap->start);
+			break;
+ 		}
 	}
 }
 
@@ -146,7 +146,8 @@ int init_first_pager(struct pager *pager,
 
 	/* Initialize ktcb */
 	task_init_registers(task, pager->start_vma);
-	task_setup_utcb(task, pager);
+
+	pager_init_utcb(task, pager);
 
 	/* Allocate space structure */
 	if (!(space = alloc_space()))
@@ -215,7 +216,7 @@ int init_pager(struct pager *pager, struct container *cont)
 
 	task_init_registers(task, pager->start_vma);
 
-	task_setup_utcb(task, pager);
+	pager_init_utcb(task, pager);
 
 	task->space = address_space_create(0);
 

src/generic/scheduler.c

@@ -274,7 +274,7 @@ static inline void context_switch(struct ktcb *next)
 	arch_hardware_flush(TASK_PGD(next));
 
 	/* Update utcb region for next task */
-	task_update_utcb(cur, next);
+	task_update_utcb(next);
 
 	/* Switch context */
 	arch_switch(cur, next);

src/generic/tcb.c

@@ -156,10 +156,10 @@ unsigned int syscall_regs_offset = offsetof(struct ktcb, syscall_regs);
  * 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)
+void task_update_utcb(struct ktcb *task)
 {
 	/* Update the KIP pointer */
-	kip.utcb = next->utcb_address;
+	kip.utcb = task->utcb_address;
 }
 
 /*

src/glue/arm/init.c

@@ -188,9 +188,6 @@ void kip_init()
 	/* KIP + 0xFF0 is pointer to UTCB segment start address */
 	utcb_ref = (struct utcb **)((unsigned long)&kip + UTCB_KIP_OFFSET);
 
-	/* All thread utcbs are allocated starting from UTCB_AREA_START */
-	*utcb_ref = (struct utcb *)UTCB_AREA_START;
-
 	add_boot_mapping(virt_to_phys(&kip), USER_KIP_PAGE, PAGE_SIZE,
 			 MAP_USR_RO_FLAGS);
 	printk("%s: Kernel built on %s, %s\n", __KERNELNAME__,