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Subject[(take 2)patch 5/7] Notify page fault call chain for sparc64
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 <anil.s.keshavamurthy@intel.com>


---
arch/sparc64/mm/fault.c | 36 +++++++++++++++++++++++++++++++++++-
include/asm-sparc64/kdebug.h | 2 ++
2 files changed, 37 insertions(+), 1 deletion(-)
Index: linux-2.6.17-rc1-mm3/arch/sparc64/mm/fault.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/arch/sparc64/mm/fault.c
+++ linux-2.6.17-rc1-mm3/arch/sparc64/mm/fault.c
@@ -31,6 +31,40 @@
#include <asm/kdebug.h>
#include <asm/mmu_context.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
+
/*
* To debug kernel to catch accesses to certain virtual/physical addresses.
* Mode = 0 selects physical watchpoints, mode = 1 selects virtual watchpoints.
@@ -263,7 +297,7 @@ asmlinkage void __kprobes do_sparc64_fau

fault_code = get_thread_fault_code();

- if (notify_die(DIE_PAGE_FAULT, "page_fault", regs,
+ if (notify_page_fault(DIE_PAGE_FAULT, "page_fault", regs,
fault_code, 0, SIGSEGV) == NOTIFY_STOP)
return;

Index: linux-2.6.17-rc1-mm3/include/asm-sparc64/kdebug.h
===================================================================
--- linux-2.6.17-rc1-mm3.orig/include/asm-sparc64/kdebug.h
+++ linux-2.6.17-rc1-mm3/include/asm-sparc64/kdebug.h
@@ -17,6 +17,8 @@ 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 sparc64die_chain;

extern void bad_trap(struct pt_regs *, long);
--
-
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