From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5B36C04AB6 for ; Fri, 31 May 2019 09:05:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B432526660 for ; Fri, 31 May 2019 09:05:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727048AbfEaJFM (ORCPT ); Fri, 31 May 2019 05:05:12 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:48266 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726240AbfEaJFM (ORCPT ); Fri, 31 May 2019 05:05:12 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 93933341; Fri, 31 May 2019 02:05:11 -0700 (PDT) Received: from [10.162.42.223] (p8cg001049571a15.blr.arm.com [10.162.42.223]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 143BB3F59C; Fri, 31 May 2019 02:05:08 -0700 (PDT) Subject: Re: [PATCH 4/4] arm64/mm: Drop vm_fault_t argument from __do_page_fault() To: Mark Rutland Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , James Morse , Andrey Konovalov References: <1559133285-27986-1-git-send-email-anshuman.khandual@arm.com> <1559133285-27986-5-git-send-email-anshuman.khandual@arm.com> <20190529151134.GH31777@lakrids.cambridge.arm.com> From: Anshuman Khandual Message-ID: <5e565fd3-0d2b-31a5-8644-c91ccc5fb05e@arm.com> Date: Fri, 31 May 2019 14:35:23 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190529151134.GH31777@lakrids.cambridge.arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/29/2019 08:41 PM, Mark Rutland wrote: > On Wed, May 29, 2019 at 06:04:45PM +0530, Anshuman Khandual wrote: >> __do_page_fault() is over complicated with multiple goto statements. This >> cleans up code flow and while there drops the vm_fault_t argument. >> Signed-off-by: Anshuman Khandual >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Mark Rutland >> Cc: James Morse >> Cc: Andrey Konovalov >> --- >> arch/arm64/mm/fault.c | 38 ++++++++++++++++---------------------- >> 1 file changed, 16 insertions(+), 22 deletions(-) >> >> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c >> index 170c71f..a53a30e 100644 >> --- a/arch/arm64/mm/fault.c >> +++ b/arch/arm64/mm/fault.c >> @@ -397,37 +397,31 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re >> static vm_fault_t __do_page_fault(struct mm_struct *mm, unsigned long addr, >> unsigned int mm_flags, unsigned long vm_flags) >> { >> - struct vm_area_struct *vma; >> - vm_fault_t fault; >> + struct vm_area_struct *vma = find_vma(mm, addr); >> >> - vma = find_vma(mm, addr); >> - fault = VM_FAULT_BADMAP; >> if (unlikely(!vma)) >> - goto out; >> - if (unlikely(vma->vm_start > addr)) >> - goto check_stack; >> + return VM_FAULT_BADMAP; >> >> /* >> - * Ok, we have a good vm_area for this memory access, so we can handle >> - * it. >> + * Check if the VMA has got the required permssion with respect >> + * to the access fault here. >> */ > > We already had a perfectly good comment for this check: > > /* > * Check that the permissions on the VMA allow for the fault which > * occurred. > */ > > ... so please keep that and minimize the diff. Sure, will keep all the existing comments here. > >> -good_area: >> + if (!(vma->vm_flags & vm_flags)) >> + return VM_FAULT_BADACCESS; >> + >> /* >> - * Check that the permissions on the VMA allow for the fault which >> - * occurred. >> + * There is a valid VMA for this access. But before proceeding >> + * make sure that it has required flags if there is an attempt >> + * to expand the stack downwards. >> */ > > I think we can drop this comment, given we didn't have it previously. Okay. > >> - if (!(vma->vm_flags & vm_flags)) { >> - fault = VM_FAULT_BADACCESS; >> - goto out; >> - } >> + if (unlikely(vma->vm_start > addr)) { >> + if (!(vma->vm_flags & VM_GROWSDOWN)) >> + return VM_FAULT_BADMAP; >> >> + if (expand_stack(vma, addr)) >> + return VM_FAULT_BADMAP; > > You can drop the line space between these two if statements. Will do. > >> + } >> return handle_mm_fault(vma, addr & PAGE_MASK, mm_flags); >> - >> -check_stack: >> - if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr)) >> - goto good_area; >> -out: >> - return fault; > > We used to check the stack before the checknig the rest of the vm_flags, > so this changes the precedence of the VM_FAULT_BADMAP and > VM_FAULT_BADACCESS return codes. > > Please check the stack before checking the other vm_flags. Though it makes some sense to move VMA permission check earlier in the function as it is the quicker one but I understand need to maintain the existing code flow in a clean up patch like this. Will retain the existing flow.