kprobes: Introduce kprobes jump optimization

Introduce kprobes jump optimization arch-independent parts.
Kprobes uses breakpoint instruction for interrupting execution
flow, on some architectures, it can be replaced by a jump
instruction and interruption emulation code. This gains kprobs'
performance drastically.

To enable this feature, set CONFIG_OPTPROBES=y (default y if the
arch supports OPTPROBE).

Changes in v9:
 - Fix a bug to optimize probe when enabling.
 - Check nearby probes can be optimize/unoptimize when disarming/arming
   kprobes, instead of registering/unregistering. This will help
   kprobe-tracer because most of probes on it are usually disabled.

Changes in v6:
 - Cleanup coding style for readability.
 - Add comments around get/put_online_cpus().

Changes in v5:
 - Use get_online_cpus()/put_online_cpus() for avoiding text_mutex
   deadlock.
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Anders Kaseorg <andersk@ksplice.com>
Cc: Tim Abbott <tabbott@ksplice.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Mathieu Desnoyers <compudj@krystal.dyndns.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
LKML-Reference: <20100225133407.6725.81992.stgit@localhost6.localdomain6>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/Kconfig

@@ -57,6 +57,17 @@ config KPROBES
 	  for kernel debugging, non-intrusive instrumentation and testing.
 	  If in doubt, say "N".
 
+config OPTPROBES
+	bool "Kprobes jump optimization support (EXPERIMENTAL)"
+	default y
+	depends on KPROBES
+	depends on !PREEMPT
+	depends on HAVE_OPTPROBES
+	select KALLSYMS_ALL
+	help
+	  This option will allow kprobes to optimize breakpoint to
+	  a jump for reducing its overhead.
+
 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 	bool
 	help
@@ -99,6 +110,8 @@ config HAVE_KPROBES
 config HAVE_KRETPROBES
 	bool
 
+config HAVE_OPTPROBES
+	bool
 #
 # An arch should select this if it provides all these things:
 #

include/linux/kprobes.h

@@ -122,6 +122,11 @@ struct kprobe {
 /* Kprobe status flags */
 #define KPROBE_FLAG_GONE	1 /* breakpoint has already gone */
 #define KPROBE_FLAG_DISABLED	2 /* probe is temporarily disabled */
+#define KPROBE_FLAG_OPTIMIZED	4 /*
+				   * probe is really optimized.
+				   * NOTE:
+				   * this flag is only for optimized_kprobe.
+				   */
 
 /* Has this kprobe gone ? */
 static inline int kprobe_gone(struct kprobe *p)
@@ -134,6 +139,12 @@ static inline int kprobe_disabled(struct kprobe *p)
 {
 	return p->flags & (KPROBE_FLAG_DISABLED | KPROBE_FLAG_GONE);
 }
+
+/* Is this kprobe really running optimized path ? */
+static inline int kprobe_optimized(struct kprobe *p)
+{
+	return p->flags & KPROBE_FLAG_OPTIMIZED;
+}
 /*
  * Special probe type that uses setjmp-longjmp type tricks to resume
  * execution at a specified entry with a matching prototype corresponding
@@ -249,6 +260,31 @@ extern kprobe_opcode_t *get_insn_slot(void);
 extern void free_insn_slot(kprobe_opcode_t *slot, int dirty);
 extern void kprobes_inc_nmissed_count(struct kprobe *p);
 
+#ifdef CONFIG_OPTPROBES
+/*
+ * Internal structure for direct jump optimized probe
+ */
+struct optimized_kprobe {
+	struct kprobe kp;
+	struct list_head list;	/* list for optimizing queue */
+	struct arch_optimized_insn optinsn;
+};
+
+/* Architecture dependent functions for direct jump optimization */
+extern int arch_prepared_optinsn(struct arch_optimized_insn *optinsn);
+extern int arch_check_optimized_kprobe(struct optimized_kprobe *op);
+extern int arch_prepare_optimized_kprobe(struct optimized_kprobe *op);
+extern void arch_remove_optimized_kprobe(struct optimized_kprobe *op);
+extern int  arch_optimize_kprobe(struct optimized_kprobe *op);
+extern void arch_unoptimize_kprobe(struct optimized_kprobe *op);
+extern kprobe_opcode_t *get_optinsn_slot(void);
+extern void free_optinsn_slot(kprobe_opcode_t *slot, int dirty);
+extern int arch_within_optimized_kprobe(struct optimized_kprobe *op,
+					unsigned long addr);
+
+extern void opt_pre_handler(struct kprobe *p, struct pt_regs *regs);
+#endif /* CONFIG_OPTPROBES */
+
 /* Get the kprobe at this addr (if any) - called with preemption disabled */
 struct kprobe *get_kprobe(void *addr);
 void kretprobe_hash_lock(struct task_struct *tsk,