[PATCH] Notify page fault call chain for sparc64

Overloading of page fault notification with the notify_die() has performance
issues(since the only interested components for page fault is kprobes and/or
kdb) and hence this patch introduces the new notifier call chain exclusively
for page fault notifications their by avoiding notifying unnecessary
components in the do_page_fault() code path.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/sparc64/mm/fault.c

@@ -31,6 +31,40 @@
 #include <asm/kdebug.h>
 #include <asm/mmu_context.h>
 
+#ifdef CONFIG_KPROBES
+ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
+
+/* Hook to register for page fault notifications */
+int register_page_fault_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
+}
+
+int unregister_page_fault_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
+}
+
+static inline int notify_page_fault(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	struct die_args args = {
+		.regs = regs,
+		.str = str,
+		.err = err,
+		.trapnr = trap,
+		.signr = sig
+	};
+	return atomic_notifier_call_chain(&notify_page_fault_chain, val, &args);
+}
+#else
+static inline int notify_page_fault(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	return NOTIFY_DONE;
+}
+#endif
+
 /*
  * To debug kernel to catch accesses to certain virtual/physical addresses.
  * Mode = 0 selects physical watchpoints, mode = 1 selects virtual watchpoints.
@@ -263,7 +297,7 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
 
 	fault_code = get_thread_fault_code();
 
-	if (notify_die(DIE_PAGE_FAULT, "page_fault", regs,
+	if (notify_page_fault(DIE_PAGE_FAULT, "page_fault", regs,
 		       fault_code, 0, SIGSEGV) == NOTIFY_STOP)
 		return;
 

include/asm-sparc64/kdebug.h

@@ -17,6 +17,8 @@ struct die_args {
 
 extern int register_die_notifier(struct notifier_block *);
 extern int unregister_die_notifier(struct notifier_block *);
+extern int register_page_fault_notifier(struct notifier_block *);
+extern int unregister_page_fault_notifier(struct notifier_block *);
 extern struct atomic_notifier_head sparc64die_chain;
 
 extern void bad_trap(struct pt_regs *, long);