[POWERPC] kprobes: Eliminate sstep exception if instruction can be emulated

For cases when probes are placed on instructions that can be emulated,
don't take the single-step exception.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

2 files changed, 40 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index dd2886f97e98..ef647e7a9dc3 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -59,12 +59,14 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
         }
 
         if (!ret) {
-                memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+                memcpy(p->ainsn.insn, p->addr,
+                                MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
                 p->opcode = *p->addr;
                 flush_icache_range((unsigned long)p->ainsn.insn,
                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
         }
 
+        p->ainsn.boostable = 0;
         return ret;
 }
 
@@ -232,6 +234,38 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
                 return 1;
 
 ss_probe:
+        if (p->ainsn.boostable >= 0) {
+                unsigned int insn = *p->ainsn.insn;
+
+                /* regs->nip is also adjusted if emulate_step returns 1 */
+                ret = emulate_step(regs, insn);
+                if (ret > 0) {
+                        /*
+                         * Once this instruction has been boosted
+                         * successfully, set the boostable flag
+                         */
+                        if (unlikely(p->ainsn.boostable == 0))
+                                p->ainsn.boostable = 1;
+
+                        if (p->post_handler)
+                                p->post_handler(p, regs, 0);
+
+                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
+                        reset_current_kprobe();
+                        preempt_enable_no_resched();
+                        return 1;
+                } else if (ret < 0) {
+                        /*
+                         * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
+                         * So, we should never get here... but, its still
+                         * good to catch them, just in case...
+                         */
+                        printk("Can't step on instruction %x\n", insn);
+                        BUG();
+                } else if (ret == 0)
+                        /* This instruction can't be boosted */
+                        p->ainsn.boostable = -1;
+        }
         prepare_singlestep(p, regs);
         kcb->kprobe_status = KPROBE_HIT_SS;
         return 1;
diff --git a/include/asm-powerpc/kprobes.h b/include/asm-powerpc/kprobes.h
index 3a5dd492588f..f850ca7020ed 100644
--- a/include/asm-powerpc/kprobes.h
+++ b/include/asm-powerpc/kprobes.h
@@ -87,6 +87,11 @@ extern void arch_remove_kprobe(struct kprobe *p);
 struct arch_specific_insn {
         /* copy of original instruction */
         kprobe_opcode_t *insn;
+        /*
+         * Set in kprobes code, initially to 0. If the instruction can be
+         * eumulated, this is set to 1, if not, to -1.
+         */
+        int boostable;
 };
 
 struct prev_kprobe {