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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 46D23C433B4 for ; Thu, 13 May 2021 18:09:57 +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 01B566143C for ; Thu, 13 May 2021 18:09:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 01B566143C 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.127028.238682 (Exim 4.92) (envelope-from ) id 1lhFmK-0004BM-Ep; Thu, 13 May 2021 18:09:44 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 127028.238682; Thu, 13 May 2021 18:09:44 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhFmK-0004BF-B7; Thu, 13 May 2021 18:09:44 +0000 Received: by outflank-mailman (input) for mailman id 127028; Thu, 13 May 2021 18:09:43 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhFmI-0004B9-Uj for xen-devel@lists.xenproject.org; Thu, 13 May 2021 18:09:42 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhFmH-00086d-FI; Thu, 13 May 2021 18:09:41 +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 1lhFmH-0005NU-8r; Thu, 13 May 2021 18:09:41 +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=MgLoHA2k7GO7Z2EQR8jSmJY7nUTs06X7ED5K0XMm7d4=; b=V2sHJkHKzRz+7GgsfdF0/MPgIR r3cXFZ979bLKcQdgiw3ruSXb4mpm2UTd5AERp6vnXp+vJoY9faYDoNZ3+eSPwmAsMOGTEhGiyAcTA 1jbvxQQu66kNp5HRVUAz5Xh4h537l7K39jksCtkcco25c0Q7U7Eo/U3WY5bS+W8x338g=; Subject: Re: [PATCH RFCv2 10/15] xen/arm: mm: Allocate xen page tables in domheap rather than xenheap 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 References: <20210425201318.15447-1-julien@xen.org> <20210425201318.15447-11-julien@xen.org> From: Julien Grall Message-ID: <9429bec0-8706-42b9-cda6-77adde961235@xen.org> Date: Thu, 13 May 2021 19:09:39 +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 Stefano, On 12/05/2021 23:44, Stefano Stabellini wrote: > On Sun, 25 Apr 2021, Julien Grall wrote: >> From: Julien Grall >> >> xen_{un,}map_table() already uses the helper to map/unmap pages >> on-demand (note this is currently a NOP on arm64). So switching to >> domheap don't have any disavantage. >> >> But this as the benefit: >> - to keep the page tables unmapped if an arch decided to do so >> - reduce xenheap use on arm32 which can be pretty small >> >> Signed-off-by: Julien Grall > > Thanks for the patch. It looks OK but let me ask a couple of questions > to clarify my doubts. > > This change should have no impact to arm64, right? > > For arm32, I wonder why we were using map_domain_page before in > xen_map_table: it wasn't necessary, was it? In fact, one could even say > that it was wrong? In xen_map_table() we need to be able to map pages from Xen binary, xenheap... On arm64, we would be able to use mfn_to_virt() because everything is mapped in Xen. But that's not the case on arm32. So we need a way to map anything easily. The only difference between xenheap and domheap are the former is always mapped while the latter may not be. So one can also view a xenheap page as a glorified domheap. I also don't really want to create yet another interface to map pages (we have vmap(), map_domain_page(), map_domain_global_page()...). So, when I implemented xen_map_table() a couple of years ago, I came to the conclusion that this is a convenient (ab)use of the interface. Cheers, -- Julien Grall