[PATCH] 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 <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 38 insertions, 2 deletions

diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
index bd6fe96cc16d..6ee7faaf2c1b 100644
--- a/arch/i386/mm/fault.c
+++ b/arch/i386/mm/fault.c
@@ -30,6 +30,40 @@
 
 extern void die(const char *,struct pt_regs *,long);
 
+#ifdef CONFIG_KPROBES
+ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
+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
+
+
 /*
  * Unlock any spinlocks which will prevent us from getting the
  * message out 
@@ -324,7 +358,7 @@ fastcall void __kprobes do_page_fault(struct pt_regs *regs,
         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;
                 /*
@@ -334,7 +368,7 @@ fastcall void __kprobes do_page_fault(struct pt_regs *regs,
                 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 --git a/include/asm-i386/kdebug.h b/include/asm-i386/kdebug.h
index 96d0828ce096..d18cdb9fc9a6 100644
--- a/include/asm-i386/kdebug.h
+++ b/include/asm-i386/kdebug.h
@@ -19,6 +19,8 @@ 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 i386die_chain;