From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3wslDy4T8qzDq8c for ; Wed, 21 Jun 2017 09:59:14 +1000 (AEST) Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v5KNwiiL121413 for ; Tue, 20 Jun 2017 19:59:12 -0400 Received: from e19.ny.us.ibm.com (e19.ny.us.ibm.com [129.33.205.209]) by mx0b-001b2d01.pphosted.com with ESMTP id 2b70yc35fw-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 20 Jun 2017 19:59:12 -0400 Received: from localhost by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 20 Jun 2017 19:59:11 -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 In-Reply-To: Message-Id: <20170620235858.GM17588@ram.oc3035372033.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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