[PATCH] Notify page fault call chain for powerpc

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, 37 insertions, 1 deletions

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index fdbba4206d59..a0a9e1e0061e 100644
--- a/arch/powerpc/mm/fault.c
+++ b/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_regs *regs, unsigned long address,
         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;
 
diff --git a/include/asm-powerpc/kdebug.h b/include/asm-powerpc/kdebug.h
index c01786ab5fa6..532bfee934f4 100644
--- a/include/asm-powerpc/kdebug.h
+++ b/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. */