[PATCH] powerpc: minor fault path optimization

[Christoph Hellwig]

Call the kprobes pagefault handler directly instead of going through
the complex notifier chain.


Signed-off-by: Christoph Hellwig <[EMAIL PROTECTED]>

Index: linux-2.6/arch/powerpc/mm/fault.c
===================================================================
--- linux-2.6.orig/arch/powerpc/mm/fault.c      2007-03-23 20:07:28.000000000 
+0100
+++ linux-2.6/arch/powerpc/mm/fault.c   2007-04-30 11:33:36.000000000 +0200
@@ -39,37 +39,26 @@
 #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)
+#ifdef CONFIG_KPROBES
+static inline int notify_page_fault(struct pt_regs *regs)
 {
-       return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
-}
+       int ret = 0;
 
-int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-       return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
-}
+       /* kprobe_running() needs smp_processor_id() */
+       if (!user_mode(regs)) {
+               preempt_disable();
+               if (kprobe_running() && kprobe_fault_handler(regs, 11))
+                       ret = 1;
+               preempt_enable();
+       }
 
-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);
+       return ret;
 }
 #else
-static inline int notify_page_fault(enum die_val val, const char *str,
-                       struct pt_regs *regs, long err, int trap, int sig)
+static inline int notify_page_fault(struct pt_regs *regs)
 {
-       return NOTIFY_DONE;
+       return 0;
 }
 #endif
 
@@ -175,8 +164,7 @@ int __kprobes do_page_fault(struct pt_re
        is_write = error_code & ESR_DST;
 #endif /* CONFIG_4xx || CONFIG_BOOKE */
 
-       if (notify_page_fault(DIE_PAGE_FAULT, "page_fault", regs, error_code,
-                               11, SIGSEGV) == NOTIFY_STOP)
+       if (notify_page_fault(regs))
                return 0;
 
        if (trap == 0x300) {
Index: linux-2.6/arch/powerpc/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/kprobes.c        2007-04-02 
20:18:18.000000000 +0200
+++ linux-2.6/arch/powerpc/kernel/kprobes.c     2007-04-30 11:33:36.000000000 
+0200
@@ -376,7 +376,7 @@ out:
        return 1;
 }
 
-static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 {
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
@@ -461,14 +461,6 @@ int __kprobes kprobe_exceptions_notify(s
                if (post_kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
-       case DIE_PAGE_FAULT:
-               /* kprobe_running() needs smp_processor_id() */
-               preempt_disable();
-               if (kprobe_running() &&
-                   kprobe_fault_handler(args->regs, args->trapnr))
-                       ret = NOTIFY_STOP;
-               preempt_enable();
-               break;
        default:
                break;
        }
Index: linux-2.6/include/asm-powerpc/kdebug.h
===================================================================
--- linux-2.6.orig/include/asm-powerpc/kdebug.h 2007-03-23 20:07:29.000000000 
+0100
+++ linux-2.6/include/asm-powerpc/kdebug.h      2007-04-30 11:51:04.000000000 
+0200
@@ -18,8 +18,20 @@ 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 *);
+
+/*
+ * These are only here because kprobes.c wants them to implement a
+ * blatant layering violation.  Will hopefully go away soon once all
+ * architectures are updated.
+ */
+static inline int register_page_fault_notifier(struct notifier_block *nb)
+{
+       return 0;
+}
+static inline int unregister_page_fault_notifier(struct notifier_block *nb)
+{
+       return 0;
+}
 extern struct atomic_notifier_head powerpc_die_chain;
 
 /* Grossly misnamed. */
@@ -29,7 +41,6 @@ enum die_val {
        DIE_DABR_MATCH,
        DIE_BPT,
        DIE_SSTEP,
-       DIE_PAGE_FAULT,
 };
 
 static inline int notify_die(enum die_val val,char *str,struct pt_regs 
*regs,long err,int trap, int sig)
Index: linux-2.6/include/asm-powerpc/kprobes.h
===================================================================
--- linux-2.6.orig/include/asm-powerpc/kprobes.h        2007-02-11 
08:17:32.000000000 +0100
+++ linux-2.6/include/asm-powerpc/kprobes.h     2007-04-30 11:33:36.000000000 
+0200
@@ -105,5 +105,6 @@ struct kprobe_ctlblk {
 
 extern int kprobe_exceptions_notify(struct notifier_block *self,
                                        unsigned long val, void *data);
+extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_KPROBES_H */
-
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