kprobes/x86: Boost probes when reentering

Integrate prepare_singlestep() into setup_singlestep() to boost
up reenter probes, if possible.

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: <20100225133423.6725.12071.stgit@localhost6.localdomain6>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/kprobes.c

@@ -406,18 +406,6 @@ static void __kprobes restore_btf(void)
 		update_debugctlmsr(current->thread.debugctlmsr);
 }
 
-static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
-{
-	clear_btf();
-	regs->flags |= X86_EFLAGS_TF;
-	regs->flags &= ~X86_EFLAGS_IF;
-	/* single step inline if the instruction is an int3 */
-	if (p->opcode == BREAKPOINT_INSTRUCTION)
-		regs->ip = (unsigned long)p->addr;
-	else
-		regs->ip = (unsigned long)p->ainsn.insn;
-}
-
 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 				      struct pt_regs *regs)
 {
@@ -430,19 +418,38 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 }
 
 static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs,
-				       struct kprobe_ctlblk *kcb)
+				       struct kprobe_ctlblk *kcb, int reenter)
 {
 #if !defined(CONFIG_PREEMPT)
 	if (p->ainsn.boostable == 1 && !p->post_handler) {
 		/* Boost up -- we can execute copied instructions directly */
-		reset_current_kprobe();
+		if (!reenter)
+			reset_current_kprobe();
+		/*
+		 * Reentering boosted probe doesn't reset current_kprobe,
+		 * nor set current_kprobe, because it doesn't use single
+		 * stepping.
+		 */
 		regs->ip = (unsigned long)p->ainsn.insn;
 		preempt_enable_no_resched();
 		return;
 	}
 #endif
-	prepare_singlestep(p, regs);
-	kcb->kprobe_status = KPROBE_HIT_SS;
+	if (reenter) {
+		save_previous_kprobe(kcb);
+		set_current_kprobe(p, regs, kcb);
+		kcb->kprobe_status = KPROBE_REENTER;
+	} else
+		kcb->kprobe_status = KPROBE_HIT_SS;
+	/* Prepare real single stepping */
+	clear_btf();
+	regs->flags |= X86_EFLAGS_TF;
+	regs->flags &= ~X86_EFLAGS_IF;
+	/* single step inline if the instruction is an int3 */
+	if (p->opcode == BREAKPOINT_INSTRUCTION)
+		regs->ip = (unsigned long)p->addr;
+	else
+		regs->ip = (unsigned long)p->ainsn.insn;
 }
 
 /*
@@ -456,11 +463,8 @@ static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
 	switch (kcb->kprobe_status) {
 	case KPROBE_HIT_SSDONE:
 	case KPROBE_HIT_ACTIVE:
-		save_previous_kprobe(kcb);
-		set_current_kprobe(p, regs, kcb);
 		kprobes_inc_nmissed_count(p);
-		prepare_singlestep(p, regs);
-		kcb->kprobe_status = KPROBE_REENTER;
+		setup_singlestep(p, regs, kcb, 1);
 		break;
 	case KPROBE_HIT_SS:
 		/* A probe has been hit in the codepath leading up to, or just
@@ -535,13 +539,13 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 			 * more here.
 			 */
 			if (!p->pre_handler || !p->pre_handler(p, regs))
-				setup_singlestep(p, regs, kcb);
+				setup_singlestep(p, regs, kcb, 0);
 			return 1;
 		}
 	} else if (kprobe_running()) {
 		p = __get_cpu_var(current_kprobe);
 		if (p->break_handler && p->break_handler(p, regs)) {
-			setup_singlestep(p, regs, kcb);
+			setup_singlestep(p, regs, kcb, 0);
 			return 1;
 		}
 	} /* else: not a kprobe fault; let the kernel handle it */