Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752840AbdFTX7O (ORCPT ); Tue, 20 Jun 2017 19:59:14 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42035 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752425AbdFTX7M (ORCPT ); Tue, 20 Jun 2017 19:59:12 -0400 Date: Tue, 20 Jun 2017 16:58:58 -0700 From: Ram Pai To: Anshuman Khandual Cc: Michael Ellerman , linux-kernel@vger.kernel.org, dave.hansen@intel.com, paulus@samba.org, aneesh.kumar@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org Subject: Re: [RFC v2 10/12] powerpc: Read AMR only if pkey-violation caused the exception. Reply-To: Ram Pai References: <1497671564-20030-1-git-send-email-linuxram@us.ibm.com> <1497671564-20030-11-git-send-email-linuxram@us.ibm.com> <87bmpkuti2.fsf@concordia.ellerman.id.au> <20170619175919.GD5845@ram.oc3035372033.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) X-TM-AS-GCONF: 00 x-cbid: 17062023-0056-0000-0000-0000038F4B21 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007263; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00877664; UDB=6.00437233; IPR=6.00657802; BA=6.00005432; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015904; XFM=3.00000015; UTC=2017-06-20 23:59:09 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17062023-0057-0000-0000-000007C561DC Message-Id: <20170620235858.GM17588@ram.oc3035372033.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-06-20_12:,, 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=8.0.1-1703280000 definitions=main-1706200412 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1533 Lines: 38 On Tue, Jun 20, 2017 at 12:16:40PM +0530, Anshuman Khandual wrote: > On 06/19/2017 11:29 PM, Ram Pai wrote: > > On Mon, Jun 19, 2017 at 09:06:13PM +1000, Michael Ellerman wrote: > >> Ram Pai writes: > >> > >>> Signed-off-by: Ram Pai > >>> --- > >>> arch/powerpc/kernel/exceptions-64s.S | 16 ++++++++++------ > >>> 1 file changed, 10 insertions(+), 6 deletions(-) > >>> > >>> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S > >>> index 8db9ef8..a4de1b4 100644 > >>> --- a/arch/powerpc/kernel/exceptions-64s.S > >>> +++ b/arch/powerpc/kernel/exceptions-64s.S > >>> @@ -493,13 +493,15 @@ EXC_COMMON_BEGIN(data_access_common) > >>> ld r12,_MSR(r1) > >>> ld r3,PACA_EXGEN+EX_DAR(r13) > >>> lwz r4,PACA_EXGEN+EX_DSISR(r13) > >>> + std r3,_DAR(r1) > >>> + std r4,_DSISR(r1) > >>> #ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS > >>> + andis. r0,r4,DSISR_KEYFAULT@h /* save AMR only if its a key fault */ > >>> + beq+ 1f > >> > >> This seems to be incremental on top of one of your other patches. > >> > >> But I don't see why, can you please just squash this into whatever patch > >> adds this code in the first place. > > > > It was an optimization added later. But yes it can be squashed into an > > earlier patch. > > Could you please explain what is the optimization this achieves ? Don't want to read the AMR if it is not a key protection fault. This is a hot-hot-path. A few cycles saved can accumulate into signficant savings overall. RP