powerpc/kprobes: Invoke handlers directly

Invoke the kprobe handlers directly rather than through notify_die(), to
reduce path taken for handling kprobes. Similar to commit 6f6343f53d
("kprobes/x86: Call exception handlers directly from do_int3/do_debug").

While at it, rename post_kprobe_handler() to kprobe_post_handler() for
more uniform naming.

Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/kprobes.h

@@ -32,6 +32,7 @@
 #include <asm/probes.h>
 #include <asm/code-patching.h>
 
+#ifdef CONFIG_KPROBES
 #define  __ARCH_WANT_KPROBES_INSN_SLOT
 
 struct pt_regs;
@@ -127,5 +128,11 @@ 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);
+extern int kprobe_handler(struct pt_regs *regs);
+extern int kprobe_post_handler(struct pt_regs *regs);
+#else
+static inline int kprobe_handler(struct pt_regs *regs) { return 0; }
+static inline int kprobe_post_handler(struct pt_regs *regs) { return 0; }
+#endif /* CONFIG_KPROBES */
 #endif /* __KERNEL__ */
 #endif	/* _ASM_POWERPC_KPROBES_H */

arch/powerpc/kernel/kprobes.c

@@ -140,13 +140,16 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 	regs->link = (unsigned long)kretprobe_trampoline;
 }
 
-static int __kprobes kprobe_handler(struct pt_regs *regs)
+int __kprobes kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p;
 	int ret = 0;
 	unsigned int *addr = (unsigned int *)regs->nip;
 	struct kprobe_ctlblk *kcb;
 
+	if (user_mode(regs))
+		return 0;
+
 	/*
 	 * We don't want to be preempted for the entire
 	 * duration of kprobe processing
@@ -359,12 +362,12 @@ static int __kprobes trampoline_probe_handler(struct kprobe *p,
  * single-stepped a copy of the instruction.  The address of this
  * copy is p->ainsn.insn.
  */
-static int __kprobes post_kprobe_handler(struct pt_regs *regs)
+int __kprobes kprobe_post_handler(struct pt_regs *regs)
 {
 	struct kprobe *cur = kprobe_running();
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 
-	if (!cur)
+	if (!cur || user_mode(regs))
 		return 0;
 
 	/* make sure we got here for instruction we have a kprobe on */
@@ -470,25 +473,7 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 				       unsigned long val, void *data)
 {
-	struct die_args *args = (struct die_args *)data;
+	return NOTIFY_DONE;
-	int ret = NOTIFY_DONE;
-
-	if (args->regs && user_mode(args->regs))
-		return ret;
-
-	switch (val) {
-	case DIE_BPT:
-		if (kprobe_handler(args->regs))
-			ret = NOTIFY_STOP;
-		break;
-	case DIE_SSTEP:
-		if (post_kprobe_handler(args->regs))
-			ret = NOTIFY_STOP;
-		break;
-	default:
-		break;
-	}
-	return ret;
 }
 
 unsigned long arch_deref_entry_point(void *entry)

arch/powerpc/kernel/traps.c

@@ -64,6 +64,7 @@
 #include <asm/asm-prototypes.h>
 #include <asm/hmi.h>
 #include <sysdev/fsl_pci.h>
+#include <asm/kprobes.h>
 
 #if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
 int (*__debugger)(struct pt_regs *regs) __read_mostly;
@@ -826,6 +827,9 @@ void single_step_exception(struct pt_regs *regs)
 
 	clear_single_step(regs);
 
+	if (kprobe_post_handler(regs))
+		return;
+
 	if (notify_die(DIE_SSTEP, "single_step", regs, 5,
 					5, SIGTRAP) == NOTIFY_STOP)
 		goto bail;
@@ -1179,6 +1183,9 @@ void program_check_exception(struct pt_regs *regs)
 		if (debugger_bpt(regs))
 			goto bail;
 
+		if (kprobe_handler(regs))
+			goto bail;
+
 		/* trap exception */
 		if (notify_die(DIE_BPT, "breakpoint", regs, 5, 5, SIGTRAP)
 				== NOTIFY_STOP)
@@ -1747,6 +1754,9 @@ void DebugException(struct pt_regs *regs, unsigned long debug_status)
 			return;
 		}
 
+		if (kprobe_post_handler(regs))
+			return;
+
 		if (notify_die(DIE_SSTEP, "block_step", regs, 5,
 			       5, SIGTRAP) == NOTIFY_STOP) {
 			return;
@@ -1761,6 +1771,9 @@ void DebugException(struct pt_regs *regs, unsigned long debug_status)
 		/* Clear the instruction completion event */
 		mtspr(SPRN_DBSR, DBSR_IC);
 
+		if (kprobe_post_handler(regs))
+			return;
+
 		if (notify_die(DIE_SSTEP, "single_step", regs, 5,
 			       5, SIGTRAP) == NOTIFY_STOP) {
 			return;