hw: use kernel signal API for page-fault signals

Instead of using the Genode user-level signal API to signal page-faults to
a page-fault handler, use the kernel API directly. Thereby the accounting
of signal contexts needed for each paging subject can be done easily.

Fix #956

repos/base-hw/src/core/include/kernel/signal_receiver.h

@@ -270,7 +270,7 @@ class Kernel::Signal_context : public Kernel::Object
 		 */
 		static capid_t syscall_create(void * p,
 		                              Signal_receiver * const receiver,
-		                              unsigned const imprint)
+		                              addr_t const imprint)
 		{
 			return call(call_id_new_signal_context(), (Call_arg)p,
 			            (Call_arg)receiver, (Call_arg)imprint);

repos/base-hw/src/core/include/pager.h

@@ -20,6 +20,8 @@
 #include <base/signal.h>
 #include <pager/capability.h>
 #include <unmanaged_singleton.h>
+#include <kernel/signal_receiver.h>
+#include <object.h>
 
 namespace Genode
 {
@@ -124,54 +126,17 @@ class Genode::Ipc_pager
 		void set_reply_mapping(Mapping m);
 };
 
-class Genode::Pager_object : public Object_pool<Pager_object>::Entry,
+class Genode::Pager_object
-                             public Signal_context
+: public Object_pool<Pager_object>::Entry,
+  public Genode::Kernel_object<Kernel::Signal_context>
 {
 	friend class Pager_entrypoint;
 
 	private:
 
-		Signal_context_capability _signal_context_cap;
 		Thread_capability   _thread_cap;
-		bool                      _signal_valid;
-		char                      _signal_buf[sizeof(Signal)];
 		unsigned long const _badge;
 
-		/**
-		 * Remember an incoming fault for handling
-		 *
-		 * \param s  fault signal
-		 */
-		void _take_fault(Signal const & s)
-		{
-			new (_signal_buf) Signal(s);
-			_signal_valid = 1;
-		}
-
-		/**
-		 * End handling of current fault
-		 */
-		void _end_fault()
-		{
-			_signal()->~Signal();
-			_signal_valid = 0;
-		}
-
-		/**
-		 * End handling of current fault if there is one
-		 */
-		void _end_fault_if_pending()
-		{
-			if (_signal_valid) { _end_fault(); }
-		}
-
-
-		/***************
-		 ** Accessors **
-		 ***************/
-
-		Signal * _signal() const;
-
 	public:
 
 		/**
@@ -181,18 +146,6 @@ class Genode::Pager_object : public Object_pool<Pager_object>::Entry,
 		 */
 		Pager_object(unsigned const badge, Affinity::Location);
 
-		/**
-		 * The faulter has caused a fault and awaits paging
-		 *
-		 * \param s  signal that communicated the fault
-		 */
-		void fault_occured(Signal const & s) { _take_fault(s); }
-
-		/**
-		 * Current fault has been resolved so resume faulter
-		 */
-		void fault_resolved() { _end_fault(); }
-
 		/**
 		 * User identification of pager object
 		 */
@@ -211,25 +164,9 @@ class Genode::Pager_object : public Object_pool<Pager_object>::Entry,
 		/**
 		 * Install information that is necessary to handle page faults
 		 *
-		 * \param c  linkage between signal context and a signal receiver
+		 * \param receiver  signal receiver that receives the page faults
-		 * \param p  linkage between pager object and a pager entry-point
 		 */
-		void start_paging(Signal_context_capability const & c,
+		void start_paging(Kernel::Signal_receiver * receiver);
-		                  Pager_capability const & p)
-		{
-			_signal_context_cap = c;
-			Object_pool<Pager_object>::Entry::cap(p);
-		}
-
-		/**
-		 * Uninstall paging information and cancel unresolved faults
-		 */
-		void stop_paging()
-		{
-			Object_pool<Pager_object>::Entry::cap(Native_capability());
-			_signal_context_cap = Signal_context_capability();
-			_end_fault_if_pending();
-		}
 
 		/**
 		 * Called when a page-fault finally could not be resolved
@@ -259,18 +196,16 @@ class Genode::Pager_object : public Object_pool<Pager_object>::Entry,
 		Thread_capability thread_cap() const;
 
 		void thread_cap(Thread_capability const & c);
-
-		unsigned signal_context_id() const;
 };
 
-class Genode::Pager_activation_base : public Thread_base,
+class Genode::Pager_activation_base
-                                      public Signal_receiver,
+: public Thread_base,
+  public Kernel_object<Kernel::Signal_receiver>,
   public Ipc_pager
 {
 	private:
 
-		Native_capability  _cap;
+		Lock               _startup_lock;
-		Lock               _cap_valid;
 		Pager_entrypoint * _ep;
 
 	public:
@@ -304,8 +239,6 @@ class Genode::Pager_activation_base : public Thread_base,
 		 ** Accessors **
 		 ***************/
 
-		Native_capability cap();
-
 		void ep(Pager_entrypoint * const ep);
 };
 

repos/base-hw/src/core/pager.cc

@@ -66,9 +66,20 @@ Thread_capability Pager_object::thread_cap() const { return _thread_cap; }
 
 void Pager_object::thread_cap(Thread_capability const & c) { _thread_cap = c; }
 
-Signal * Pager_object::_signal() const { return (Signal *)_signal_buf; }
+void Pager_object::wake_up()
+{
+	using Object = Kernel_object<Kernel::Signal_context>;
+	Kernel::ack_signal(Object::_cap.dst());
+}
 
-void Pager_object::wake_up() { fault_resolved(); }
+void Pager_object::start_paging(Kernel::Signal_receiver * receiver)
+{
+	using Object = Kernel_object<Kernel::Signal_context>;
+	using Entry  = Object_pool<Pager_object>::Entry;
+
+	create(receiver, (unsigned long)this);
+	Entry::cap(Object::_cap);
+}
 
 void Pager_object::exception_handler(Signal_context_capability) { }
 
@@ -81,18 +92,11 @@ void Pager_object::unresolved_page_fault_occurred()
 }
 
 Pager_object::Pager_object(unsigned const badge, Affinity::Location)
-:
+: Object_pool<Pager_object>::Entry(Kernel_object<Kernel::Signal_context>::_cap),
-	_signal_valid(0),
   _badge(badge)
 { }
 
 
-unsigned Pager_object::signal_context_id() const
-{
-	return _signal_context_cap.dst();
-}
-
-
 /***************************
  ** Pager_activation_base **
  ***************************/
@@ -102,18 +106,12 @@ void Pager_activation_base::ep(Pager_entrypoint * const ep) { _ep = ep; }
 
 Pager_activation_base::Pager_activation_base(char const * const name,
                                              size_t const stack_size)
-:
+: Thread_base(0, name, stack_size),
-	Thread_base(0, name, stack_size), _cap_valid(Lock::LOCKED), _ep(0)
+  Kernel_object<Kernel::Signal_receiver>(true),
+  _startup_lock(Lock::LOCKED), _ep(0)
 { }
 
 
-Native_capability Pager_activation_base::cap()
-{
-	if (!_cap.valid()) { _cap_valid.lock(); }
-	return _cap;
-}
-
-
 /**********************
  ** Pager_entrypoint **
  **********************/
@@ -121,25 +119,18 @@ Native_capability Pager_activation_base::cap()
 void Pager_entrypoint::dissolve(Pager_object * const o)
 {
 	remove_locked(o);
-	o->stop_paging();
-	_activation->Signal_receiver::dissolve(o);
 }
 
 
 Pager_entrypoint::Pager_entrypoint(Cap_session *,
                                    Pager_activation_base * const activation)
-:
+: _activation(activation) {
-	_activation(activation)
+	_activation->ep(this); }
-{
-	_activation->ep(this);
-}
 
 
 Pager_capability Pager_entrypoint::manage(Pager_object * const o)
 {
-	Signal_context_capability scc = _activation->Signal_receiver::manage(o);
+	o->start_paging(_activation->kernel_object());
-	Pager_capability p = reinterpret_cap_cast<Pager_object>(scc);
-	o->start_paging(scc, p);
 	insert(o);
-	return p;
+	return reinterpret_cap_cast<Pager_object>(o->cap());
 }

repos/base-hw/src/core/platform_thread.cc

@@ -214,7 +214,7 @@ void Platform_thread::pager(Pager_object * const pager)
 {
 	typedef Kernel::Thread_event_id Event_id;
 	if (pager) {
-		unsigned const sc_id = pager->signal_context_id();
+		unsigned const sc_id = pager->cap().dst();
 		if (sc_id) {
 			if (!Kernel::route_thread_event(kernel_object(), Event_id::FAULT,
 			                                sc_id)) {

repos/base-hw/src/core/rm_session_support.cc

@@ -57,13 +57,13 @@ int Pager_activation_base::apply_mapping()
 void Pager_activation_base::entry()
 {
 	/* get ready to receive faults */
-	_cap = Thread_base::myself()->tid().cap;
+	_startup_lock.unlock();
-	_cap_valid.unlock();
 	while (1)
 	{
 		/* receive fault */
-		Signal s = Signal_receiver::wait_for_signal();
+		if (Kernel::await_signal(_cap.dst())) continue;
-		Pager_object * po = static_cast<Pager_object *>(s.context());
+		Pager_object * po =
+			*(Pager_object**)Thread_base::myself()->utcb()->base();
 
 		/*
 		 * Synchronize access and ensure that the object is still managed
@@ -74,9 +74,6 @@ void Pager_activation_base::entry()
 		Object_pool<Pager_object>::Guard pog(_ep->lookup_and_lock(pon));
 		if (!pog) continue;
 
-		/* let pager object go to fault state */
-		pog->fault_occured(s);
-
 		/* fetch fault data */
 		Platform_thread * const pt = (Platform_thread *)pog->badge();
 		if (!pt) {
@@ -104,6 +101,6 @@ void Pager_activation_base::entry()
 			continue;
 		}
 		/* let pager object go back to no-fault state */
-		pog->fault_resolved();
+		pog->wake_up();
 	}
 }