From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1167699AbdDXJON (ORCPT ); Mon, 24 Apr 2017 05:14:13 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57922 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1167536AbdDXJOG (ORCPT ); Mon, 24 Apr 2017 05:14:06 -0400 From: "Aneesh Kumar K.V" To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Scott Wood Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/5] powerpc/mm: Evaluate user_mode(regs) only once in do_page_fault() In-Reply-To: <592ce73ae7cbd2383740ac31e5fed5ca5beac721.1492606298.git.christophe.leroy@c-s.fr> References: <592ce73ae7cbd2383740ac31e5fed5ca5beac721.1492606298.git.christophe.leroy@c-s.fr> Date: Mon, 24 Apr 2017 14:43:02 +0530 MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-MML: disable x-cbid: 17042409-0004-0000-0000-000001F9687D X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17042409-0005-0000-0000-000009EDEFC8 Message-Id: <87r30i184h.fsf@skywalker.in.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-24_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1704240161 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy writes: > Analysis of the assembly code shows that when using user_mode(regs), > at least the 'andi.' is redone all the time, and also > the 'lwz ,132(r31)' most of the time. With the new form, the 'is_user' > is mapped to cr4, then all further use of is_user results in just > things like 'beq cr4,218 ' > > Without the patch: > > 50: 81 1e 00 84 lwz r8,132(r30) > 54: 71 09 40 00 andi. r9,r8,16384 > 58: 40 82 00 0c bne 64 > > 84: 81 3e 00 84 lwz r9,132(r30) > 8c: 71 2a 40 00 andi. r10,r9,16384 > 90: 41 a2 01 64 beq 1f4 > > d4: 81 3e 00 84 lwz r9,132(r30) > dc: 71 28 40 00 andi. r8,r9,16384 > e0: 41 82 02 08 beq 2e8 > > 108: 81 3e 00 84 lwz r9,132(r30) > 110: 71 28 40 00 andi. r8,r9,16384 > 118: 41 82 02 28 beq 340 > > 1e4: 81 3e 00 84 lwz r9,132(r30) > 1e8: 71 2a 40 00 andi. r10,r9,16384 > 1ec: 40 82 01 68 bne 354 > > 228: 81 3e 00 84 lwz r9,132(r30) > 22c: 71 28 40 00 andi. r8,r9,16384 > 230: 41 82 ff c4 beq 1f4 > > 288: 71 2a 40 00 andi. r10,r9,16384 > 294: 41 a2 fe 60 beq f4 > > 50c: 81 3e 00 84 lwz r9,132(r30) > 514: 71 2a 40 00 andi. r10,r9,16384 > 518: 40 a2 fc e0 bne 1f8 > > 534: 81 3e 00 84 lwz r9,132(r30) > 53c: 71 2a 40 00 andi. r10,r9,16384 > 540: 41 82 fc b8 beq 1f8 > > This patch creates a local var called 'is_user' which contains the > result of user_mode(regs) > > With the patch: > > 20: 81 03 00 84 lwz r8,132(r3) > 48: 55 09 97 fe rlwinm r9,r8,18,31,31 > 58: 2e 09 00 00 cmpwi cr4,r9,0 > 5c: 40 92 00 0c bne cr4,68 > > 88: 41 b2 01 90 beq cr4,218 > > d4: 40 92 01 d0 bne cr4,2a4 > > 120: 41 b2 00 f8 beq cr4,218 > > 138: 41 b2 ff a0 beq cr4,d8 > > 1d4: 40 92 00 e0 bne cr4,2b4 > Reviewed-by: Aneesh Kumar K.V > Signed-off-by: Christophe Leroy > --- > arch/powerpc/mm/fault.c | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > index b56bf472db6d..8d1639eee3af 100644 > --- a/arch/powerpc/mm/fault.c > +++ b/arch/powerpc/mm/fault.c > @@ -202,6 +202,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > int is_write = 0; > int trap = TRAP(regs); > int is_exec = trap == 0x400; > + int is_user = user_mode(regs); > int fault; > int rc = 0; > unsigned int inst = 0; > @@ -244,7 +245,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > * The kernel should never take an execute fault nor should it > * take a page fault to a kernel address. > */ > - if (!user_mode(regs) && (is_exec || (address >= TASK_SIZE))) { > + if (!is_user && (is_exec || (address >= TASK_SIZE))) { > rc = SIGSEGV; > goto bail; > } > @@ -263,7 +264,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > local_irq_enable(); > > if (faulthandler_disabled() || mm == NULL) { > - if (!user_mode(regs)) { > + if (!is_user) { > rc = SIGSEGV; > goto bail; > } > @@ -284,10 +285,10 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > * can result in fault, which will cause a deadlock when called with > * mmap_sem held > */ > - if (is_write && user_mode(regs)) > + if (is_write && is_user) > __get_user(inst, (unsigned int __user *)regs->nip); > > - if (user_mode(regs)) > + if (is_user) > flags |= FAULT_FLAG_USER; > > /* When running in the kernel we expect faults to occur only to > @@ -306,7 +307,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > * thus avoiding the deadlock. > */ > if (!down_read_trylock(&mm->mmap_sem)) { > - if (!user_mode(regs) && !search_exception_tables(regs->nip)) > + if (!is_user && !search_exception_tables(regs->nip)) > goto bad_area_nosemaphore; > > retry: > @@ -506,7 +507,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > > bad_area_nosemaphore: > /* User mode accesses cause a SIGSEGV */ > - if (user_mode(regs)) { > + if (is_user) { > _exception(SIGSEGV, regs, code, address); > goto bail; > } > -- > 2.12.0