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 C2926C43334 for ; Tue, 5 Jul 2022 09:53:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EF14C6B0071; Tue, 5 Jul 2022 05:52:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EA1AB6B0073; Tue, 5 Jul 2022 05:52:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D69776B0074; Tue, 5 Jul 2022 05:52:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id C492F6B0071 for ; Tue, 5 Jul 2022 05:52:44 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 8A57160779 for ; Tue, 5 Jul 2022 09:52:44 +0000 (UTC) X-FDA: 79652581848.15.7A64865 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf02.hostedemail.com (Postfix) with ESMTP id 2BD2480006 for ; Tue, 5 Jul 2022 09:52:43 +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 E3FBC61994; Tue, 5 Jul 2022 09:52:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8C206C341C7; Tue, 5 Jul 2022 09:52:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1657014762; bh=9MTPdYNRD6u5hC7g7ZiQEjDmfdWtcP6Y0Ap52ScAOrU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=E+0G79QBInSietGAYHA+UwbA3SZdfOhuaklndufor9FZUA6khw3anhHUNDoGOHD3B OiNjMC0GZjnUkxas6g5DGYAsuZ/RnPNtExcsDV8q2J8RuM44nwYY1vDlloERd60WZh YKZlVgWUyfbZ4xKkyhFBQygOwhkVVcWBSixfQsmF+VGDJ0GohzgQWAE81Alg2zj2zx C70oiDFt5aiNCbRzP9yWU3+vZYKu4lPp3Xfr1kKLd5Mh+2vWJJhvZdawLdZUY4fHNP LF7WtnHGD4S0ApNQOLCA5bgA7XycFTlf0uTwsCjGWQIh5wKFOP+TKdHTZCj30wY0M+ kIDCKPPpyGxgg== Date: Tue, 5 Jul 2022 10:52:34 +0100 From: Will Deacon To: Ard Biesheuvel Cc: "guanghui.fgh" , baolin.wang@linux.alibaba.com, catalin.marinas@arm.com, 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, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation Message-ID: <20220705095231.GB552@willie-the-truck> References: <20220704103523.GC31437@willie-the-truck> <73f0c53b-fd17-c5e9-3773-1d71e564eb50@linux.alibaba.com> <20220704111402.GA31553@willie-the-truck> <4accaeda-572f-f72d-5067-2d0999e4d00a@linux.alibaba.com> <20220704131516.GC31684@willie-the-truck> <2ae1cae0-ee26-aa59-7ed9-231d67194dce@linux.alibaba.com> <20220704142313.GE31684@willie-the-truck> <6977c692-78ca-5a67-773e-0389c85f2650@linux.alibaba.com> <20220704163815.GA32177@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=E+0G79QB; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of will@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=will@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657014764; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=gcgP8qcEw9Gr+M5bsAWN9wb93s5ePqrwZQqM//j1Tuw=; b=zOpFUfg2c5mb1T2qdBSooqnrxOSbzUnuECNbM8zaNImYLm6fWfh1N5PUhbu2iWtDGe+c4b l0hNB0bGaltUHAea92MWb8vWecjQLALNMMK484swNsA094p8AqbBFpWxLKE6Ah5QwOYna7 yAG6VLutj1c/xohe/Km2DJs1PCB/UWI= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657014764; a=rsa-sha256; cv=none; b=u6+Vg+4VDFKWaa+/IHaR9ePDnSLTD7YbOX0OaxQ7J3MqSa4GYz463Gtl9wcO57xcMTj9ex Ps/hSnLX9ZnXUDCgxGkfr3P/spRPgpLEtKYbHFzBnsjwp9dl8bAUAJG/8+vV/mFxNDhMoj B9/+GPiphiEyFnkAC4ShdmunCUnQMr8= X-Stat-Signature: rgnmbmur599hhgwpdcpeaxxnd4epj1xn X-Rspamd-Queue-Id: 2BD2480006 Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=E+0G79QB; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of will@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=will@kernel.org X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1657014763-231563 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 Mon, Jul 04, 2022 at 07:09:23PM +0200, Ard Biesheuvel wrote: > On Mon, 4 Jul 2022 at 18:38, Will Deacon wrote: > > > > On Mon, Jul 04, 2022 at 10:34:07PM +0800, guanghui.fgh wrote: > > > Thanks. > > > > > > 在 2022/7/4 22:23, Will Deacon 写道: > > > > On Mon, Jul 04, 2022 at 10:11:27PM +0800, guanghui.fgh wrote: > ... > > > > > Namely, it's need to use non block/section mapping for crashkernel mem > > > > > before shringking. > > > > > > > > Well, yes, but we can change arch_kexec_[un]protect_crashkres() not to do > > > > that if we're leaving the thing mapped, no? > > > > > > > I think we should use arch_kexec_[un]protect_crashkres for crashkernel mem. > > > > > > Because when invalid crashkernel mem pagetable, there is no chance to rd/wr > > > the crashkernel mem by mistake. > > > > > > If we don't use arch_kexec_[un]protect_crashkres to invalid crashkernel mem > > > pagetable, there maybe some write operations to these mem by mistake which > > > may cause crashkernel boot error and vmcore saving error. > > > > I don't really buy this line of reasoning. The entire main kernel is > > writable, so why do we care about protecting the crashkernel so much? The > > _code_ to launch the crash kernel is writable! If you care about preventing > > writes to memory which should not be writable, then you should use > > rodata=full. > > > > This is not entirely true - the core kernel text and rodata are > remapped r/o in the linear map, whereas all module code and rodata are > left writable when rodata != full. Yes, sorry, you're quite right. The kernel text is only writable if rodata=off. But I still think it makes sense to protect the crashkernel only if rodata=full (which is the default on arm64) as this allows us to rely on page mappings and I think fits well with what we do for modules. > But the conclusion is the same, imo: if you can't be bothered to > protect a good chunk of the code and rodata that the kernel relies on, > why should the crashkernel be treated any differently? Thanks. Will