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Subject[(resend)patch 2/7] Notify page fault call chain for x86_64
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>

---
arch/x86_64/kernel/traps.c | 12 ++++++++++++
arch/x86_64/mm/fault.c | 4 ++--
include/asm-x86_64/kdebug.h | 16 ++++++++++++++++
3 files changed, 30 insertions(+), 2 deletions(-)
Index: linux-2.6.17-rc1-mm3/arch/x86_64/kernel/traps.c
===================================================================
--- linux-2.6.17-rc1-mm3.orig/arch/x86_64/kernel/traps.c
+++ linux-2.6.17-rc1-mm3/arch/x86_64/kernel/traps.c
@@ -71,6 +71,7 @@ asmlinkage void machine_check(void);
asmlinkage void spurious_interrupt_bug(void);

ATOMIC_NOTIFIER_HEAD(die_chain);
+ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);

int register_die_notifier(struct notifier_block *nb)
{
@@ -85,6 +86,17 @@ int unregister_die_notifier(struct notif
}
EXPORT_SYMBOL(unregister_die_notifier);

+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 void conditional_sti(struct pt_regs *regs)
{
if (regs->eflags & X86_EFLAGS_IF)
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
@@ -348,7 +348,7 @@ 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 +358,7 @@ 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
@@ -15,7 +15,10 @@ 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;
+extern struct atomic_notifier_head notify_page_fault_chain;

/* Grossly misnamed. */
enum die_val {
@@ -47,6 +50,19 @@ static inline int notify_die(enum die_va
return atomic_notifier_call_chain(&die_chain, val, &args);
}

+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);
+}
+
extern int printk_address(unsigned long address);
extern void die(const char *,struct pt_regs *,long);
extern void __die(const char *,struct pt_regs *,long);
--
-
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