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 86AE8C433ED for ; Thu, 22 Apr 2021 15:24:11 +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 20A0361425 for ; Thu, 22 Apr 2021 15:24:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 20A0361425 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com 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.115644.220682 (Exim 4.92) (envelope-from ) id 1lZbBM-0002MO-0y; Thu, 22 Apr 2021 15:23:56 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 115644.220682; Thu, 22 Apr 2021 15:23:55 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lZbBL-0002MH-UI; Thu, 22 Apr 2021 15:23:55 +0000 Received: by outflank-mailman (input) for mailman id 115644; Thu, 22 Apr 2021 15:23:55 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lZbBL-0002MC-Br for xen-devel@lists.xenproject.org; Thu, 22 Apr 2021 15:23:55 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 7ce4c605-bca0-4e08-8136-d193db8d8cf0; Thu, 22 Apr 2021 15:23:54 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 77B9BAD8A; Thu, 22 Apr 2021 15:23:53 +0000 (UTC) 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" X-Inumbo-ID: 7ce4c605-bca0-4e08-8136-d193db8d8cf0 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1619105033; h=from:from:reply-to: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=2Y9p6wqTZTpAuq62nsYavt+Zc+iTEKfVNYhmCcTHSvQ=; b=ZKyT31pPnQGrhTHT6hyXQqNpkpth0+n/Q0Y7MkQ6POt6kyMIBgWt43T/8NdOPLBBsa/q/X /JunfNY+sdKkGqDNYsOCgMMJOq1R2B/5DPIfZNdbJlg+WaavWcW0Vztxkq5eqe95bwpsa8 lqITg0PyYLTCyuqvrYD4RbK0ptvemHM= Subject: Re: [PATCH 0/3] xen: remove some checks for always present Xen features To: Juergen Gross Cc: Boris Ostrovsky , Stefano Stabellini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Peter Zijlstra , linux-kernel@vger.kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org References: <20210422151007.2205-1-jgross@suse.com> From: Jan Beulich Message-ID: <08e3fcf1-dabc-c550-f76c-47a78a12274b@suse.com> Date: Thu, 22 Apr 2021 17:23:53 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 22.04.2021 17:17, Juergen Gross wrote: > On 22.04.21 17:16, Jan Beulich wrote: >> On 22.04.2021 17:10, Juergen Gross wrote: >>> Some features of Xen can be assumed to be always present, so add a >>> central check to verify this being true and remove the other checks. >>> >>> Juergen Gross (3): >>> xen: check required Xen features >>> xen: assume XENFEAT_mmu_pt_update_preserve_ad being set for pv guests >>> xen: assume XENFEAT_gnttab_map_avail_bits being set for pv guests >> >> I wonder whether it's a good idea to infer feature presence from >> version numbers. If (at some point in the past) you had inferred >> gnttab v2 being available by version, this would have been broken >> by its availability becoming controllable by a command line option >> in Xen. > > I'm testing the feature to be really present when booting and issue a > message if it is not there. And how does this help if the feature really isn't there yet other code assumes it is? Jan