[(resend)patch 1/7] Notify page fault call chain for i386

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 <[email protected]>

---
 arch/i386/kernel/traps.c  |   12 ++++++++++++
 arch/i386/mm/fault.c      |    4 ++--
 include/asm-i386/kdebug.h |   15 +++++++++++++++
 3 files changed, 29 insertions(+), 2 deletions(-)

Index: linux-2.6.17-rc1-mm3/arch/i386/kernel/traps.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/arch/i386/kernel/traps.c
+++ linux-2.6.17-rc1-mm3/arch/i386/kernel/traps.c
@@ -93,6 +93,7 @@ asmlinkage void machine_check(void);
 
 static int kstack_depth_to_print = 24;
 ATOMIC_NOTIFIER_HEAD(i386die_chain);
+ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
 
 int register_die_notifier(struct notifier_block *nb)
 {
@@ -107,6 +108,17 @@ int unregister_die_notifier(struct notif
 }
 EXPORT_SYMBOL(unregister_die_notifier);
 
+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 valid_stack_ptr(struct thread_info *tinfo, void *p)
 {
 	return	p > (void *)tinfo &&
Index: linux-2.6.17-rc1-mm3/arch/i386/mm/fault.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/arch/i386/mm/fault.c
+++ linux-2.6.17-rc1-mm3/arch/i386/mm/fault.c
@@ -321,7 +321,7 @@ fastcall void __kprobes do_page_fault(st
 	if (unlikely(address >= TASK_SIZE)) {
 		if (!(error_code & 0x0000000d) && 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;
 		/*
@@ -331,7 +331,7 @@ fastcall void __kprobes do_page_fault(st
 		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;
 
Index: linux-2.6.17-rc1-mm3/include/asm-i386/kdebug.h
===================================================================
--- linux-2.6.17-rc1-mm3.orig/include/asm-i386/kdebug.h
+++ linux-2.6.17-rc1-mm3/include/asm-i386/kdebug.h
@@ -19,7 +19,10 @@ 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 i386die_chain;
+extern struct atomic_notifier_head notify_page_fault_chain;
 
 
 /* Grossly misnamed. */
@@ -53,4 +56,16 @@ static inline int notify_die(enum die_va
 	return atomic_notifier_call_chain(&i386die_chain, val, &args);
 }
 
+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);
+}
 #endif

--
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    • From: Anil S Keshavamurthy <[email protected]>

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