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,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 619EDC433ED for ; Sat, 15 May 2021 09:21:39 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 10BD26054E for ; Sat, 15 May 2021 09:21:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 10BD26054E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.127706.240029 (Exim 4.92) (envelope-from ) id 1lhqU6-00050T-Vj; Sat, 15 May 2021 09:21:22 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 127706.240029; Sat, 15 May 2021 09:21:22 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhqU6-00050M-Sf; Sat, 15 May 2021 09:21:22 +0000 Received: by outflank-mailman (input) for mailman id 127706; Sat, 15 May 2021 09:21:21 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhqU5-00050G-Oh for xen-devel@lists.xenproject.org; Sat, 15 May 2021 09:21:21 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhqU2-0003qJ-2m; Sat, 15 May 2021 09:21:18 +0000 Received: from [54.239.6.185] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1lhqU1-00078p-R3; Sat, 15 May 2021 09:21:17 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=EXjVYPGzAzSOgIsaYooiVOnwHh36GTNnxdAwU9E4nqw=; b=JTiNl9w90dS7vIsPPbGOY/6QkX dSZ7Wxu1ITWzWc8cM156+WCliA840fRIufu9fdXEMRe7wezPbiyMoAIzykKHLgFEQdd+IEr0Xnawe EvTSGn4z1o7Cx5ITkk33PoI382eqsDFLVSP2SfztXsm28/e3lKtiS6yQ9D9VwoBaowrA=; Subject: Re: [PATCH RFCv2 14/15] xen/arm: mm: Rework setup_xenheap_mappings() To: Stefano Stabellini Cc: xen-devel@lists.xenproject.org, Wei.Chen@arm.com, Henry.Wang@arm.com, Penny.Zheng@arm.com, Bertrand.Marquis@arm.com, Julien Grall , Volodymyr Babchuk , Julien Grall References: <20210425201318.15447-1-julien@xen.org> <20210425201318.15447-15-julien@xen.org> From: Julien Grall Message-ID: <8cda6d2d-7f3c-fef6-c534-2fadabed1bad@xen.org> Date: Sat, 15 May 2021 10:21:15 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Hi, On 15/05/2021 00:51, Stefano Stabellini wrote: > On Sun, 25 Apr 2021, Julien Grall wrote: >> From: Julien Grall >> >> A few issues have been reported with setup_xenheap_mappings() over the >> last couple of years. The main ones are: >> - It will break on platform supporting more than 512GB of RAM >> because the memory allocated by the boot allocator is not yet >> mapped. >> - Aligning all the regions to 1GB may lead to unexpected result >> because we may alias non-cacheable region (such as device or reserved >> regions). >> >> map_pages_to_xen() was recently reworked to allow superpage mappings and >> deal with the use of page-tables before they are mapped. >> >> Most of the code in setup_xenheap_mappings() is now replaced with a >> single call to map_pages_to_xen(). >> >> This also require to re-order the steps setup_mm() so the regions are >> given to the boot allocator first and then we setup the xenheap >> mappings. > > I know this is paranoia but doesn't this introduce a requirement on the > size of the first bank in bootinfo.mem.bank[] ? > > It should be at least 8KB? AFAIK, the current requirement is 4KB because of the 1GB mapping. Long term, it would be 8KB. > > I know it is unlikely but it is theoretically possible to have a first > bank of just 1KB. All the page allocators are working at the page granularity level. I am not entirely sure whether the current Xen would ignore the region or break. Note that setup_xenheap_mappings() is taking a base MFN and a number of pages to map. So this doesn't look to be a new problem here. For the 8KB requirement, we can look at first all the pages to the boot allocator and then do the mapping. > > I think we should write the requirement down with an in-code comment? > Or better maybe we should write a message about it in the panic below? I can write an in-code comment but I think writing down in the panic() would be wrong because there is no promise this is going to be the only reason it fails (imagine there is a bug in the code...). Cheers, -- Julien Grall