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 B1D20C433ED for ; Thu, 22 Apr 2021 15:23:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D51F61458 for ; Thu, 22 Apr 2021 15:23:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236569AbhDVPY3 (ORCPT ); Thu, 22 Apr 2021 11:24:29 -0400 Received: from mx2.suse.de ([195.135.220.15]:37564 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236367AbhDVPY3 (ORCPT ); Thu, 22 Apr 2021 11:24:29 -0400 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= 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) 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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