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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E381C433EF for ; Fri, 1 Jul 2022 17:24:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A5DE86B0071; Fri, 1 Jul 2022 13:24:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A0DCA6B0073; Fri, 1 Jul 2022 13:24:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 924C56B0074; Fri, 1 Jul 2022 13:24:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 84AD86B0071 for ; Fri, 1 Jul 2022 13:24:38 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 5A6243441C for ; Fri, 1 Jul 2022 17:24:38 +0000 (UTC) X-FDA: 79639205436.18.7AAEC92 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf09.hostedemail.com (Postfix) with ESMTP id A193C140049 for ; Fri, 1 Jul 2022 17:24:37 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D53FE60B17; Fri, 1 Jul 2022 17:24:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78BB2C3411E; Fri, 1 Jul 2022 17:24:32 +0000 (UTC) Date: Fri, 1 Jul 2022 18:24:28 +0100 From: Catalin Marinas To: Guanghui Feng 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 Subject: Re: [PATCH v3] arm64: mm: fix linear mapping mem access performance degradation Message-ID: References: <1656586222-98555-1-git-send-email-guanghuifeng@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; 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bh=2oF/ZJdnIywYNkcmaayHmMAsPrAT2uMpJaptfbtDYoE=; b=72D4c032DmPf1Q6+GAi1Wtrhk4Iw7XL9sMfE3pUwd4o8wv6u7zeZZGoHDWR8Va9Rk15fiS 71o8gg8QzLPsSB747lgUVpja4uHUevCXaCwQbOt2aIKmTL32qn5c0rDZ4iDxwqCc+TPnTM /aKahO3kk4NvVYFYdBdfhOoWYM4Rmtk= X-Rspam-User: X-Rspamd-Server: rspam04 Authentication-Results: imf09.hostedemail.com; dkim=none; spf=pass (imf09.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) X-Stat-Signature: ik75ke9mniazi8n6gmf7q19ho4negerf X-Rspamd-Queue-Id: A193C140049 X-HE-Tag: 1656696277-306195 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. -- Catalin