linux-kernel - Re: [PATCH v3 6/7] powerpc: kprobes: emulate instructions on kprobe handler re-entry

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Date:   Wed, 19 Apr 2017 16:42:50 +0000
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ingo Molnar <mingo@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v3 6/7] powerpc: kprobes: emulate instructions on kprobe
 handler re-entry

Excerpts from Masami Hiramatsu's message of April 19, 2017 20:13:
> 
> BTW, as I pointed, 5/7 and 6/7 should be merged since this actually
> makes meaningful change.

Yes, sorry if I wasn't clear in my previous reply in the (!) previous 
patch series.

Since this has to go through the powerpc tree, I followed this since I 
felt that Michael Ellerman prefers to keep functional changes separate 
from refactoring. I'm fine with either approach.

Michael?

Thanks!
- Naveen

> 
> Thank you,
> 
> On Wed, 19 Apr 2017 18:21:05 +0530
> "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:
> 
>> On kprobe handler re-entry, try to emulate the instruction rather than
>> single stepping always.
>> 
>> Acked-by: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
>> ---
>>  arch/powerpc/kernel/kprobes.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>> 
>> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
>> index 46e8c1e03ce4..067e9863bfdf 100644
>> --- a/arch/powerpc/kernel/kprobes.c
>> +++ b/arch/powerpc/kernel/kprobes.c
>> @@ -276,6 +276,14 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
>>  			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) {
>> -- 
>> 2.12.1
>> 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@...nel.org>
> 
>