[(take 2)patch 1/7] Notify page fault call chain for x86_64

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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 <[email protected]>

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

Index: linux-2.6.17-rc1-mm3/arch/x86_64/mm/fault.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/arch/x86_64/mm/fault.c
+++ linux-2.6.17-rc1-mm3/arch/x86_64/mm/fault.c
@@ -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;
 
Index: linux-2.6.17-rc1-mm3/include/asm-x86_64/kdebug.h
===================================================================
--- linux-2.6.17-rc1-mm3.orig/include/asm-x86_64/kdebug.h
+++ linux-2.6.17-rc1-mm3/include/asm-x86_64/kdebug.h
@@ -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. */

--
-
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