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=-7.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 60611C433DF for ; Thu, 23 Jul 2020 05:23:45 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BFC5F20768 for ; Thu, 23 Jul 2020 05:23:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BFC5F20768 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ghiti.fr Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4BC12k3V1WzDqXB for ; Thu, 23 Jul 2020 15:23:42 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=ghiti.fr (client-ip=217.70.183.195; helo=relay3-d.mail.gandi.net; envelope-from=alex@ghiti.fr; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ghiti.fr Received: from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net [217.70.183.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BC10t6Q90zDr7K for ; Thu, 23 Jul 2020 15:22:04 +1000 (AEST) X-Originating-IP: 90.112.45.105 Received: from [192.168.1.14] (lfbn-gre-1-325-105.w90-112.abo.wanadoo.fr [90.112.45.105]) (Authenticated sender: alex@ghiti.fr) by relay3-d.mail.gandi.net (Postfix) with ESMTPSA id 722BD60002; Thu, 23 Jul 2020 05:21:51 +0000 (UTC) Subject: Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone To: Benjamin Herrenschmidt , Palmer Dabbelt References:

<7cb2285e-68ba-6827-5e61-e33a4b65ac03@ghiti.fr> <54af168083aee9dbda1b531227521a26b77ba2c8.camel@kernel.crashing.org> From: Alex Ghiti Message-ID: Date: Thu, 23 Jul 2020 01:21:50 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <54af168083aee9dbda1b531227521a26b77ba2c8.camel@kernel.crashing.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: aou@eecs.berkeley.edu, linux-mm@kvack.org, Anup Patel , linux-kernel@vger.kernel.org, Atish Patra , paulus@samba.org, zong.li@sifive.com, Paul Walmsley , linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Benjamin, Le 7/21/20 à 7:11 PM, Benjamin Herrenschmidt a écrit : > On Tue, 2020-07-21 at 14:36 -0400, Alex Ghiti wrote: >>>> I guess I don't understand why this is necessary at all. >>>> Specifically: why >>>> can't we just relocate the kernel within the linear map? That would >>>> let the >>>> bootloader put the kernel wherever it wants, modulo the physical >>>> memory size we >>>> support. We'd need to handle the regions that are coupled to the >>>> kernel's >>>> execution address, but we could just put them in an explicit memory >>>> region >>>> which is what we should probably be doing anyway. >>> >>> Virtual relocation in the linear mapping requires to move the kernel >>> physically too. Zong implemented this physical move in its KASLR RFC >>> patchset, which is cumbersome since finding an available physical spot >>> is harder than just selecting a virtual range in the vmalloc range. >>> >>> In addition, having the kernel mapping in the linear mapping prevents >>> the use of hugepage for the linear mapping resulting in performance loss >>> (at least for the GB that encompasses the kernel). >>> >>> Why do you find this "ugly" ? The vmalloc region is just a bunch of >>> available virtual addresses to whatever purpose we want, and as noted by >>> Zong, arm64 uses the same scheme. > > I don't get it :-) > > At least on powerpc we move the kernel in the linear mapping and it > works fine with huge pages, what is your problem there ? You rely on > punching small-page size holes in there ? > ARCH_HAS_STRICT_KERNEL_RWX prevents the use of a hugepage for the kernel mapping in the direct mapping as it sets different permissions to different part of the kernel (data, text..etc). > At least in the old days, there were a number of assumptions that > the kernel text/data/bss resides in the linear mapping. > > If you change that you need to ensure that it's still physically > contiguous and you'll have to tweak __va and __pa, which might induce > extra overhead. > Yes that's done in this patch and indeed there is an overhead to those functions. > Cheers, > Ben. > > Thanks, Alex