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=-5.8 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 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 B620EC433DB for ; Thu, 4 Mar 2021 17:13:47 +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 4932E64E45 for ; Thu, 4 Mar 2021 17:13:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4932E64E45 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=xenproject.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.93356.176250 (Exim 4.92) (envelope-from ) id 1lHrXN-0007gf-0z; Thu, 04 Mar 2021 17:13:21 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 93356.176250; Thu, 04 Mar 2021 17:13:20 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lHrXM-0007gY-UG; Thu, 04 Mar 2021 17:13:20 +0000 Received: by outflank-mailman (input) for mailman id 93356; Thu, 04 Mar 2021 17:13:19 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lHrXL-0007gR-Dk for xen-devel@lists.xenproject.org; Thu, 04 Mar 2021 17:13:19 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lHrXL-0008E1-7a for xen-devel@lists.xenproject.org; Thu, 04 Mar 2021 17:13:19 +0000 Received: from iwj (helo=mariner.uk.xensource.com) by xenbits.xenproject.org with local-bsmtp (Exim 4.92) (envelope-from ) id 1lHrXL-0003Vw-3Q for xen-devel@lists.xenproject.org; Thu, 04 Mar 2021 17:13:19 +0000 Received: from iwj by mariner.uk.xensource.com with local (Exim 4.89) (envelope-from ) id 1lHrXH-0005qi-MX; Thu, 04 Mar 2021 17:13:15 +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=xenproject.org; s=20200302mail; h=References:In-Reply-To:Subject:Cc:To:Date :Message-ID:Content-Transfer-Encoding:Content-Type:MIME-Version:From; bh=+3bPWeNO4cRWraA/arRquDBv6TCVSBgSkRs9wkbBh6g=; b=svo0Cpxu/XtfuEPluaMtfcP3Qx uFr+h31rbMDz+1728pxUp1r5xYKtVHkoVikUmiBzO04Y0vCvyJ5t9qoNIons6+UfzWjApnDikmqXY LTP8lCG8p/0ZlC9SLiRihOSIttqZgb2Ek410u+/XOevHp1iOomtBDGpW15rP7/WZRZDA=; From: Ian Jackson MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Message-ID: <24641.5419.379341.215528@mariner.uk.xensource.com> Date: Thu, 4 Mar 2021 17:13:15 +0000 To: Roger Pau =?iso-8859-1?Q?Monn=E9?= Cc: , Wei Liu , Anthony PERARD , Jan Beulich , Andrew Cooper , Jun Nakajima , "Kevin Tian" , Boris Ostrovsky Subject: Re: [PATCH v2 for-4.15] x86/msr: introduce an option for HVM relaxed rdmsr behavior In-Reply-To: References: <20210304144755.35891-1-roger.pau@citrix.com> <24640.62938.427877.757656@mariner.uk.xensource.com> <24640.64194.445736.52546@mariner.uk.xensource.com> X-Mailer: VM 8.2.0b under 24.5.1 (i686-pc-linux-gnu) Roger Pau Monné writes ("Re: [PATCH v2 for-4.15] x86/msr: introduce an option for HVM relaxed rdmsr behavior"): > On Thu, Mar 04, 2021 at 03:20:34PM +0000, Ian Jackson wrote: > > The guest could be stopped with xl shutdown and then recrated with xl > > create, from the config file. I don't think we want to break that use > > case here either. > > So my original approach was to actually risk breaking creation from > config file and require the user to set the rdmsr_relaxed option, and > report the problem upstream. I think ideally we would like to get to a > point where we could drop the rdmsr_relaxed option, but maybe that's > too optimistic. Isn't there some way we can move in this direction without the first thing that users experience being their guests not being able to be created ? Maybe we could print a warning on the console or something ? > We have done quite a lot of testing of this new policy, but obviously > it's not possible to test all possible guest OSes. Forcing the new > policy by default might be too risky, so indeed falling back to > enabling this by default could be the only solution. > > The main downside of enabling by default is that then we have to > resign to always having this kind of quirky behavior for MSR > accesses as the default. What would stop us changing the default later, when we had a better idea of the set of RDMSRs that need to be special-cased ? Ian.