linux-kernel - [PATCH 3/3] powerpc: kprobes: emulate instructions on kprobe handler re-entry

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Date:   Tue, 14 Feb 2017 14:08:03 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 3/3] powerpc: kprobes: emulate instructions on kprobe handler re-entry

On kprobe handler re-entry, try to emulate the instruction rather than
single stepping always.

As a related change, remove the duplicate saving of msr as that is
already done in set_current_kprobe()

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/kprobes.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 9cdf2de31e9e..c213637b9d25 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -206,10 +206,17 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
 			 */
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, regs, kcb);
-			kcb->kprobe_saved_msr = regs->msr;
 			kprobes_inc_nmissed_count(p);
 			prepare_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
+			if (p->ainsn.boostable >= 0) {
+				ret = try_to_emulate(p, regs);
+
+				if (ret > 0) {
+					restore_previous_kprobe(kcb);
+					return 1;
+				}
+			}
 			return 1;
 		} else {
 			if (*addr != BREAKPOINT_INSTRUCTION) {
-- 
2.11.0