From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752130AbdBCTkC (ORCPT ); Fri, 3 Feb 2017 14:40:02 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:52405 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751414AbdBCTkA (ORCPT ); Fri, 3 Feb 2017 14:40:00 -0500 Date: Sat, 4 Feb 2017 01:09:49 +0530 From: "Naveen N. Rao" To: Michael Ellerman Cc: Anju T Sudhakar , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, ananth@in.ibm.com, mahesh@linux.vnet.ibm.com, paulus@samba.org, mhiramat@kernel.org, srikar@linux.vnet.ibm.com Subject: Re: [PATCH V3 3/4] arch/powerpc: Implement Optprobes References: <1482153507-17350-1-git-send-email-anju@linux.vnet.ibm.com> <1482153507-17350-2-git-send-email-anju@linux.vnet.ibm.com> <87a8a6dvwo.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87a8a6dvwo.fsf@concordia.ellerman.id.au> User-Agent: Mutt/1.6.2 (2016-07-01) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17020319-0024-0000-0000-00000397EE00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17020319-0025-0000-0000-000011120765 Message-Id: <20170203193949.GD4090@naverao1-tp.localdomain> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-02-03_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1612050000 definitions=main-1702030185 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Michael, Thanks for the review! I'll defer to Anju on most of the aspects, but... On 2017/02/01 09:53PM, Michael Ellerman wrote: > Anju T Sudhakar writes: > > > +static void optimized_callback(struct optimized_kprobe *op, > > + struct pt_regs *regs) > > +{ > > + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); > > + unsigned long flags; > > + > > + /* This is possible if op is under delayed unoptimizing */ > > + if (kprobe_disabled(&op->kp)) > > + return; > > + > > + local_irq_save(flags); > > What is that protecting against? Because on powerpc it doesn't actually > disable interrupts, it just masks some of them, the perf interrupt for > example can still run. That's an excellent catch, as always! :) This is meant to prevent us from missing kprobe hits while processing interrupts that arrive when this optprobe is being handled. And you are totally right -- we would miss kprobe hits during PMI handling with the current approach. We need a hard_irq_disable() there. > > + /* > > + * Optprobe template: > > + * This template gets copied into one of the slots in optinsn_slot > > + * and gets fixed up with real optprobe structures et al. > > + */ > > + .global optprobe_template_entry > > +optprobe_template_entry: > > + /* Create an in-memory pt_regs */ > > + stdu r1,-INT_FRAME_SIZE(r1) > > + SAVE_GPR(0,r1) > > + /* Save the previous SP into stack */ > > + addi r0,r1,INT_FRAME_SIZE > > + std r0,GPR1(r1) > > + SAVE_10GPRS(2,r1) > > + SAVE_10GPRS(12,r1) > > + SAVE_10GPRS(22,r1) > > + /* Save SPRS */ > > + mfmsr r5 > > + std r5,_MSR(r1) > > + li r5,0x700 > > + std r5,_TRAP(r1) > > + li r5,0 > > + std r5,ORIG_GPR3(r1) > > + std r5,RESULT(r1) > > + mfctr r5 > > + std r5,_CTR(r1) > > + mflr r5 > > + std r5,_LINK(r1) > > + mfspr r5,SPRN_XER > > + std r5,_XER(r1) > > + mfcr r5 > > + std r5,_CCR(r1) > > + lbz r5,PACASOFTIRQEN(r13) > > + std r5,SOFTE(r1) > > + mfdar r5 > > + std r5,_DAR(r1) > > + mfdsisr r5 > > + std r5,_DSISR(r1) > > So this is what made me originally reply to this patch. This > save/restore sequence. > > I'm not clear on why this is what we need to save/restore. > > Aren't we essentially just interposing a function call? If so do we need > to save/restore all of these? eg. MSR/DAR/DSISR. Non-volatile GPRs? And > why are we pretending there was a 0x700 trap? > > Is it because we're going to end up emulating the instruction and so we > need everything in pt_regs ? Yes, that and also for the kprobe pre_handler() which takes pt_regs. Regards, - Naveen