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=-5.4 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 66D17C4363D for ; Tue, 22 Sep 2020 18:40:04 +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 F34BF20756 for ; Tue, 22 Sep 2020 18:40:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=xen.org header.i=@xen.org header.b="QaSm8L+f" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F34BF20756 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 localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kKnCg-000281-9r; Tue, 22 Sep 2020 18:39:50 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kKnCf-00027u-5j for xen-devel@lists.xenproject.org; Tue, 22 Sep 2020 18:39:49 +0000 X-Inumbo-ID: 2c064c75-547c-422b-a888-8c919a81bbf4 Received: from mail.xenproject.org (unknown [104.130.215.37]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 2c064c75-547c-422b-a888-8c919a81bbf4; Tue, 22 Sep 2020 18:39:48 +0000 (UTC) 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=AXl/+IYMD9MtGVFiYVEwxrW2+qdHJRqrvo91dSaX39I=; b=QaSm8L+fwveEcWbgxO69P1SAJr hhOF+H9BRBgRDU+cg2zO7S8bQr7QpJAcBAQt6wdWt5v9eANq+vH048no2YF9iXeuGHwMxxiu+EJ3R McuM/zhyw5rEUdk0X2pA3qts5KVt6vK5m4GIJ7rseL2sYlo4767k23M+C1UON/Dqj8WQ=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kKnCV-0005mC-4u; Tue, 22 Sep 2020 18:39:39 +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 1kKnCU-0006XA-Rg; Tue, 22 Sep 2020 18:39:38 +0000 Subject: Re: [PATCH v4 4/4] xen/mm: Provide dummy M2P-related helpers when !CONFIG_HAVE_M2P To: Jan Beulich Cc: xen-devel@lists.xenproject.org, Julien Grall , Stefano Stabellini , Volodymyr Babchuk , Andrew Cooper , George Dunlap , Ian Jackson , Wei Liu , Tamas K Lengyel References: <20200921180214.4842-1-julien@xen.org> <20200921180214.4842-5-julien@xen.org> <26387b5d-97f7-3c6a-ad40-94b144a3b0ae@suse.com> From: Julien Grall Message-ID: Date: Tue, 22 Sep 2020 19:39:35 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <26387b5d-97f7-3c6a-ad40-94b144a3b0ae@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Hi Jan, On 22/09/2020 09:02, Jan Beulich wrote: > On 21.09.2020 20:02, Julien Grall wrote: >> --- a/xen/include/xen/mm.h >> +++ b/xen/include/xen/mm.h >> @@ -685,4 +685,17 @@ static inline void put_page_alloc_ref(struct page_info *page) >> } >> } >> >> +/* >> + * Dummy implementation of M2P-related helpers for common code when >> + * the architecture doesn't have an M2P. >> + */ >> +#ifndef CONFIG_HAS_M2P >> + >> +#define INVALID_M2P_ENTRY (~0UL) >> +#define SHARED_M2P(_e) false >> + >> +static inline void set_gpfn_from_mfn(unsigned long mfn, unsigned long pfn) {} > > While I think this would better BUG() or at least ASSERT_UNREACHABLE(), > I realize its use in page_alloc.c prevents this. However, if this was a > macro, I think the need for having INVALID_P2M_ENTRY would vanish, as > long as the stub macro didn't evaluate its 2nd argument. This is not very future proof... The cost of defining INVALID_M2P_ENTRY is very minimal compare to the damage that may result from this choice. > I'm feeling somewhat uneasy with the SHARED_M2P() definition: This > would seem to better be tied to CONFIG_MEM_SHARING rather than M2P > existence. I can see pros and cons in both solution. To me it contains the word "M2P" so it makes sense to be protected by HAS_M2P. If someone else think that it should be protected by CONFIG_MEM_SHARING, then I will do the change. I have added Tamas to give him an opportunity to share his view. Cheers, -- Julien Grall