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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EDCFDC433EF for ; Sat, 2 Jul 2022 10:51:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230155AbiGBKsp (ORCPT ); Sat, 2 Jul 2022 06:48:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58372 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229446AbiGBKso (ORCPT ); Sat, 2 Jul 2022 06:48:44 -0400 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 53AA1AE6F for ; Sat, 2 Jul 2022 03:48:42 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R371e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045170;MF=guanghuifeng@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0VI6ToP3_1656758915; Received: from 30.39.96.230(mailfrom:guanghuifeng@linux.alibaba.com fp:SMTPD_---0VI6ToP3_1656758915) by smtp.aliyun-inc.com; Sat, 02 Jul 2022 18:48:37 +0800 Message-ID: <6dc308db-3685-4df5-506a-71f9e3794ec8@linux.alibaba.com> Date: Sat, 2 Jul 2022 18:48:35 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v3] arm64: mm: fix linear mapping mem access performance degradation To: Catalin Marinas Cc: baolin.wang@linux.alibaba.com, will@kernel.org, akpm@linux-foundation.org, david@redhat.com, jianyong.wu@arm.com, james.morse@arm.com, quic_qiancai@quicinc.com, christophe.leroy@csgroup.eu, jonathan@marek.ca, mark.rutland@arm.com, thunder.leizhen@huawei.com, anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, rppt@kernel.org, geert+renesas@glider.be, ardb@kernel.org, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com References: <1656586222-98555-1-git-send-email-guanghuifeng@linux.alibaba.com> From: "guanghui.fgh" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks. 在 2022/7/2 1:24, Catalin Marinas 写道: > On Thu, Jun 30, 2022 at 06:50:22PM +0800, Guanghui Feng wrote: >> +static void init_pmd_remap(pud_t *pudp, unsigned long addr, unsigned long end, >> + phys_addr_t phys, pgprot_t prot, >> + phys_addr_t (*pgtable_alloc)(int), int flags) >> +{ >> + unsigned long next; >> + pmd_t *pmdp; >> + phys_addr_t map_offset; >> + pmdval_t pmdval; >> + >> + pmdp = pmd_offset(pudp, addr); >> + do { >> + next = pmd_addr_end(addr, end); >> + >> + if (!pmd_none(*pmdp) && pmd_sect(*pmdp)) { >> + phys_addr_t pte_phys = pgtable_alloc(PAGE_SHIFT); >> + pmd_clear(pmdp); >> + pmdval = PMD_TYPE_TABLE | PMD_TABLE_UXN; >> + if (flags & NO_EXEC_MAPPINGS) >> + pmdval |= PMD_TABLE_PXN; >> + __pmd_populate(pmdp, pte_phys, pmdval); >> + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); > > This doesn't follow the architecture requirements for "break before > make" when changing live page tables. While it may work, it risks > triggering a TLB conflict abort. The correct sequence normally is: > > pmd_clear(); > flush_tlb_kernel_range(); > __pmd_populate(); > > However, do we have any guarantees that the kernel doesn't access the > pmd range being unmapped temporarily? The page table itself might live > in one of these sections, so set_pmd() etc. can get a translation fault. Thanks. 1. When reserving and remapping mem, there is only one boot cpu running, no other cpu/thread/process running. At the same time, only the boot cpu remap and modify linear mem mapping when there is no cpu access the same linear mapped mem(the boot cpu is rebuilding it, and other cpu have't been booted). 2.Because the kernel image and linear mem mapping are splited in two method: map_kernel and map_mem. When rebuilding the linear mem mapping(mapped by map_mem), there is no effect to the kernle image mapping. As a result, I thins there is no effect to the linear mem mapping and kernel image mapping. >