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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 5A89EC433DF for ; Tue, 19 May 2020 03:23:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 43941206D4 for ; Tue, 19 May 2020 03:23:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728154AbgESDXf (ORCPT ); Mon, 18 May 2020 23:23:35 -0400 Received: from mail.loongson.cn ([114.242.206.163]:33100 "EHLO loongson.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726302AbgESDXf (ORCPT ); Mon, 18 May 2020 23:23:35 -0400 Received: from [10.20.42.25] (unknown [10.20.42.25]) by mail.loongson.cn (Coremail) with SMTP id AQAAf9DxT90JUcNerWM2AA--.50S3; Tue, 19 May 2020 11:22:50 +0800 (CST) Subject: Re: [PATCH v3 3/3] mm/memory.c: Add memory read privilege before filling PTE entry To: Andrew Morton References: <1589778529-25627-1-git-send-email-maobibo@loongson.cn> <1589778529-25627-3-git-send-email-maobibo@loongson.cn> <20200518135747.d8837ba6742b2d193e14fbb0@linux-foundation.org> Cc: Thomas Bogendoerfer , Jiaxun Yang , Huacai Chen , Paul Burton , Dmitry Korotin , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Stafford Horne , Steven Price , Anshuman Khandual , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, Mike Rapoport , Sergei Shtylyov , "Maciej W. Rozycki" , linux-mm@kvack.org, David Hildenbrand From: maobibo Message-ID: Date: Tue, 19 May 2020 11:22:49 +0800 User-Agent: Mozilla/5.0 (X11; Linux mips64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20200518135747.d8837ba6742b2d193e14fbb0@linux-foundation.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-CM-TRANSID: AQAAf9DxT90JUcNerWM2AA--.50S3 X-Coremail-Antispam: 1UD129KBjvJXoWxCw4ktr1Dur17CFy8AFW7CFg_yoW5WF15pF Z7G3W29Fs7tw18AF1xW3WkAF15uw4FgFW5Wrn5Gw15ZwsrArn8CFW7GFWFvryDAr1UCw4r AF4Utr4UZan8uaUanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUU90b7Iv0xC_Kw4lb4IE77IF4wAFF20E14v26ryj6rWUM7CY07I2 0VC2zVCF04k26cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rw A2F7IY1VAKz4vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xII jxv20xvEc7CjxVAFwI0_Cr0_Gr1UM28EF7xvwVC2z280aVAFwI0_Gr1j6F4UJwA2z4x0Y4 vEx4A2jsIEc7CjxVAFwI0_Gr1j6F4UJwAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40E FcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr 0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY 04v7Mxk0xIA0c2IEe2xFo4CEbIxvr21l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7 v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF 1VAY17CE14v26r4a6rW5MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIx AIcVC0I7IYx2IY6xkF7I0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWrZr1j6s0D MIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIda VFxhVjvjDU0xZFpf9x07b5sjbUUUUU= X-CM-SenderInfo: xpdruxter6z05rqj20fqof0/ Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/19/2020 04:57 AM, Andrew Morton wrote: > On Mon, 18 May 2020 13:08:49 +0800 Bibo Mao wrote: > >> On mips platform, hw PTE entry valid bit is set in pte_mkyoung >> function, it is used to set physical page with readable privilege. > > pte_mkyoung() seems to be a strange place to set the pte's valid bit. > Why is it done there? Can it be done within mips's mk_pte()? On MIPS system hardware cannot set PAGE_ACCESS bit when accessing the page, software sets PAGE_ACCESS software bit and PAGE_VALID hw bit together during page fault stage. If mk_pte is called in page fault flow, it is ok to set both bits. If it is not called in page fault, PAGE_ACCESS is set however there is no actual memory accessing. > >> Here add pte_mkyoung function to make page readable on MIPS platform >> during page fault handling. This patch improves page fault latency >> about 10% on my MIPS machine with lmbench lat_pagefault case. >> >> ... >> >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -2704,6 +2704,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) >> } >> flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte)); >> entry = mk_pte(new_page, vma->vm_page_prot); >> + entry = pte_mkyoung(entry); >> entry = maybe_mkwrite(pte_mkdirty(entry), vma); > > What is the effect on non-mips machines? If it's only "additional > overhead" then it would be better to add a new pte_mkvalid() (or > whatever) and arrange for it to be a no-op on all but mips? how about adding pte_sw_mkyoung alike function which is a noop on all but mips? this function is used to set PAGE_ACCESS bit and PAGE_VALID bit on mips platform. regards bibo,mao > >> /* >> * Clear the pte entry and flush it first, before updating the >> @@ -3378,6 +3379,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) >> __SetPageUptodate(page); >> >> entry = mk_pte(page, vma->vm_page_prot); >> + entry = pte_mkyoung(entry); >> if (vma->vm_flags & VM_WRITE) >> entry = pte_mkwrite(pte_mkdirty(entry)); >> >> @@ -3660,6 +3662,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg, >> >> flush_icache_page(vma, page); >> entry = mk_pte(page, vma->vm_page_prot); >> + entry = pte_mkyoung(entry); >> if (write) >> entry = maybe_mkwrite(pte_mkdirty(entry), vma); >> /* copy-on-write page */ >> diff --git a/mm/mprotect.c b/mm/mprotect.c >> index 494192ca..673f1cd 100644 >> --- a/mm/mprotect.c >> +++ b/mm/mprotect.c >> @@ -131,6 +131,8 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, >> ptent = pte_clear_uffd_wp(ptent); >> } >> >> + if (vma->vm_flags & VM_READ) >> + ptent = pte_mkyoung(ptent); >> /* Avoid taking write faults for known dirty pages */ >> if (dirty_accountable && pte_dirty(ptent) && >> (pte_soft_dirty(ptent) ||