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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 F305CC433ED for ; Fri, 9 Apr 2021 12:07:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BBE4C61178 for ; Fri, 9 Apr 2021 12:07:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233780AbhDIMHt (ORCPT ); Fri, 9 Apr 2021 08:07:49 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34968 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233533AbhDIMHq (ORCPT ); Fri, 9 Apr 2021 08:07:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617970053; h=from:from: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; bh=cPZ0Ie5xguOPpDLkGIOIn4xg63tOXcjWUdAtpJa2pV4=; b=AYnrtV5ZdJVKk5m3RhdBd3yFvIlMXhIYBjBCH9bBpSmtOm9aTT3eFFZQNKwAh9au+2rOtq x0rj9wE6rlA/w4TUGUKUzhu++ZaydnTcgWvuBd8STsDH6ABnvn8S+qARP19o2xGUZr/kni tHRm3WbnJZ2ujdQDPAg0yTrHqXg4jq4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-47-m71PPXm6OwGvDs3bRsxdqA-1; Fri, 09 Apr 2021 08:07:29 -0400 X-MC-Unique: m71PPXm6OwGvDs3bRsxdqA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E92AA801971; Fri, 9 Apr 2021 12:07:27 +0000 (UTC) Received: from [10.36.115.11] (ovpn-115-11.ams2.redhat.com [10.36.115.11]) by smtp.corp.redhat.com (Postfix) with ESMTP id 75E3460916; Fri, 9 Apr 2021 12:07:25 +0000 (UTC) To: Alex Ghiti , Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Cc: Vitaly Wool , Mike Rapoport References: <20210409065115.11054-1-alex@ghiti.fr> <3500f3cb-b660-5bbc-ae8d-0c9770e4a573@ghiti.fr> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v7] RISC-V: enable XIP Message-ID: Date: Fri, 9 Apr 2021 14:07:24 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09.04.21 13:39, Alex Ghiti wrote: > Hi David, > > Le 4/9/21 à 4:23 AM, David Hildenbrand a écrit : >> On 09.04.21 09:14, Alex Ghiti wrote: >>> Le 4/9/21 à 2:51 AM, Alexandre Ghiti a écrit : >>>> From: Vitaly Wool >>>> >>>> Introduce XIP (eXecute In Place) support for RISC-V platforms. >>>> It allows code to be executed directly from non-volatile storage >>>> directly addressable by the CPU, such as QSPI NOR flash which can >>>> be found on many RISC-V platforms. This makes way for significant >>>> optimization of RAM footprint. The XIP kernel is not compressed >>>> since it has to run directly from flash, so it will occupy more >>>> space on the non-volatile storage. The physical flash address used >>>> to link the kernel object files and for storing it has to be known >>>> at compile time and is represented by a Kconfig option. >>>> >>>> XIP on RISC-V will for the time being only work on MMU-enabled >>>> kernels. >>>> >>> I added linux-mm and linux-arch to get feedbacks because I noticed that >>> DEBUG_VM_PGTABLE fails for SPARSEMEM (it works for FLATMEM but I think >>> it does not do what is expected): the fact that we don't have any struct >>> page to back the text and rodata in flash is the problem but to which >>> extent ? >> >> Just wondering, why can't we create a memmap for that memory -- or is it >> even desireable to not do that explicity? There might be some nasty side >> effects when not having a memmap for text and rodata. > > > Do you have examples of such effects ? Any feature that will not work > without that ? > At least if it's not part of /proc/iomem in any way (maybe "System RAM" is not what we want without a memmap, TBD), kexec-tools won't be able to handle it properly e.g., for kdump. But not sure if that is really relevant in your setup. Regarding other features, anything that does a pfn_valid(), pfn_to_page() or pfn_to_online_page() would behave differently now -- assuming the kernel doesn't fall into a section with other System RAM (whereby we would still allocate the memmap for the whole section). I guess you might stumble over some surprises in some code paths, but nothing really comes to mind. Not sure if your zeropage is part of the kernel image on RISC-V (I remember that we sometimes need a memmap there, but I might be wrong)? I assume you still somehow create the direct mapping for the kernel, right? So it's really some memory region with a direct mapping but without a memmap (and right now, without a resource), correct? [...] >> >> Also, will that memory properly be exposed in the resource tree as >> System RAM (e.g., /proc/iomem) ? Otherwise some things (/proc/kcore) >> won't work as expected - the kernel won't be included in a dump. > > > I have just checked and it does not appear in /proc/iomem. > > Ok your conclusion would be to have struct page, I'm going to implement > this version then using memblock as you described. Let's first evaluate what the harm could be. You could (and should?) create the kernel resource manually - IIRC, that's independent of the memmap/memblock thing. @Mike, what's your take on not having a memmap for kernel text and ro data? -- Thanks, David / dhildenb