[(take 2)patch 4/7] Notify page fault call chain for powerpc

[Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>]

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.

Changes since previous version:
1) Moved the implementaion of register/unregister_page_fault_notifier()
call to arch/xxx/mm/fault.c
2) Added #ifdef CONFIG_KPROBES around this register/unregister calls
as currently kprobes is the only potential user.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>


---
 arch/powerpc/mm/fault.c      |   36 +++++++++++++++++++++++++++++++++++-
 include/asm-powerpc/kdebug.h |    2 ++
 2 files changed, 37 insertions(+), 1 deletion(-)

Index: linux-2.6.17-rc1-mm3/arch/powerpc/mm/fault.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/arch/powerpc/mm/fault.c
+++ linux-2.6.17-rc1-mm3/arch/powerpc/mm/fault.c
@@ -40,6 +40,40 @@
 #include <asm/kdebug.h>
 #include <asm/siginfo.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
+
 /*
  * Check whether the instruction at regs->nip is a store using
  * an update addressing form which will update r1.
@@ -142,7 +176,7 @@ int __kprobes do_page_fault(struct pt_re
 	is_write = error_code & ESR_DST;
 #endif /* CONFIG_4xx || CONFIG_BOOKE */
 
-	if (notify_die(DIE_PAGE_FAULT, "page_fault", regs, error_code,
+	if (notify_page_fault(DIE_PAGE_FAULT, "page_fault", regs, error_code,
 				11, SIGSEGV) == NOTIFY_STOP)
 		return 0;
 
Index: linux-2.6.17-rc1-mm3/include/asm-powerpc/kdebug.h
===================================================================
--- linux-2.6.17-rc1-mm3.orig/include/asm-powerpc/kdebug.h
+++ linux-2.6.17-rc1-mm3/include/asm-powerpc/kdebug.h
@@ -18,6 +18,8 @@ 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 powerpc_die_chain;
 
 /* Grossly misnamed. */

--
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