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,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 0F86FC433B4 for ; Thu, 20 May 2021 09:45:50 +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 CAC4F6199B for ; Thu, 20 May 2021 09:45:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CAC4F6199B 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.130854.244883 (Exim 4.92) (envelope-from ) id 1ljfFN-0003am-FG; Thu, 20 May 2021 09:45:41 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 130854.244883; Thu, 20 May 2021 09:45:41 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ljfFN-0003af-Bo; Thu, 20 May 2021 09:45:41 +0000 Received: by outflank-mailman (input) for mailman id 130854; Thu, 20 May 2021 09:45:39 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ljfFL-0003aY-P4 for xen-devel@lists.xenproject.org; Thu, 20 May 2021 09:45:39 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ljfFL-0005QE-Iy; Thu, 20 May 2021 09:45:39 +0000 Received: from [54.239.6.186] (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 1ljfFL-0004CE-CY; Thu, 20 May 2021 09:45:39 +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=BxH/GFn0fN7kXTcFiXRVG8uCM4g0mwU6q07w/M/m7Ig=; b=LQggWTT7QNPSJkC2L4mkw2h258 ULqC1ytNIYweLOOH0uDGIzk4eq8TSPSfGzswD0cOxn8oVMQi8kekz3B80yoi4pn8OE7QakA+BMXkW 1ld1H6ZzzmMjJ56sWY6OFpijZs1EJWuxMWJCy4ynRizhsXImMUQ3C/QrQ7AHzbR2lz9M=; Subject: Re: [PATCH 03/10] xen/arm: introduce PGC_reserved To: Jan Beulich , Penny Zheng Cc: Bertrand Marquis , Wei Chen , nd , "xen-devel@lists.xenproject.org" , "sstabellini@kernel.org" References: <20210518052113.725808-1-penny.zheng@arm.com> <20210518052113.725808-4-penny.zheng@arm.com> <2f4eb08e-261b-70c4-bcbc-e08db36a50a9@xen.org> <44b46f35-cc51-9274-77f2-cfd18c998a38@xen.org> From: Julien Grall Message-ID: <4b36ce2c-e60f-8974-fa5b-b8f2261e25ad@xen.org> Date: Thu, 20 May 2021 10:45:37 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 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 Jan, On 20/05/2021 10:27, Jan Beulich wrote: > On 20.05.2021 10:59, Julien Grall wrote: >> On 20/05/2021 09:40, Penny Zheng wrote: >>> Oh, Second thought on this. >>> And I think you are referring to balloon in/out here, hmm, also, like >> >> Yes I am referring to balloon in/out. >> >>> I replied there: >>> "For issues on ballooning out or in, it is not supported here. >> >> So long you are not using the solution in prod then you are fine (see >> below)... But then we should make clear this feature is a tech preview. >> >>> Domain on Static Allocation and 1:1 direct-map are all based on >>> dom0-less right now, so no PV, grant table, event channel, etc, considered. >>> >>> Right now, it only supports device got passthrough into the guest." >> >> So we are not creating the hypervisor node in the DT for dom0less domU. >> However, the hypercalls are still accessible by a domU if it really >> wants to use them. >> >> Therefore, a guest can easily mess up with your static configuration and >> predictability. >> >> IMHO, this is a must to solve before "static memory" can be used in >> production. > > I'm having trouble seeing why it can't be addressed right away: It can be solved right away. Dom0less domUs don't officially know they are running on Xen (they could bruteforce it though), so I think it would be fine to merge without it for a tech preview. > Such > guests can balloon in only after they've ballooned out some pages, > and such balloon-in requests would be satisfied from the same static > memory that is associated by the guest anyway. This would require some bookeeping to know the page was used previously. But nothing very challenging though. Cheers, -- Julien Grall