From: 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.

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

 arch/x86_64/mm/fault.c      |   39 ++++++++++++++++++++++++++++++++--
 include/asm-x86_64/kdebug.h |    2 +
 2 files changed, 39 insertions(+), 2 deletions(-)

diff -puN arch/x86_64/mm/fault.c~notify-page-fault-call-chain-for-x86_64 arch/x86_64/mm/fault.c
--- devel/arch/x86_64/mm/fault.c~notify-page-fault-call-chain-for-x86_64	2006-04-20 23:29:56.000000000 -0700
+++ devel-akpm/arch/x86_64/mm/fault.c	2006-04-20 23:29:56.000000000 -0700
@@ -41,6 +41,41 @@
 #define PF_RSVD	(1<<3)
 #define PF_INSTR	(1<<4)
 
+#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)
+{
+	vmalloc_sync_all();
+	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
+
 void bust_spinlocks(int yes)
 {
 	int loglevel_save = console_loglevel;
@@ -348,7 +383,7 @@ asmlinkage void __kprobes do_page_fault(
 			if (vmalloc_fault(address) >= 0)
 				return;
 		}
-		if (notify_die(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
+		if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
 						SIGSEGV) == NOTIFY_STOP)
 			return;
 		/*
@@ -358,7 +393,7 @@ asmlinkage void __kprobes do_page_fault(
 		goto bad_area_nosemaphore;
 	}
 
-	if (notify_die(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
+	if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
 					SIGSEGV) == NOTIFY_STOP)
 		return;
 
diff -puN include/asm-x86_64/kdebug.h~notify-page-fault-call-chain-for-x86_64 include/asm-x86_64/kdebug.h
--- devel/include/asm-x86_64/kdebug.h~notify-page-fault-call-chain-for-x86_64	2006-04-20 23:29:56.000000000 -0700
+++ devel-akpm/include/asm-x86_64/kdebug.h	2006-04-20 23:29:56.000000000 -0700
@@ -15,6 +15,8 @@ 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 die_chain;
 
 /* Grossly misnamed. */
_