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 714B2C433E0 for ; Fri, 19 Feb 2021 16:17:08 +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 35C2464EC0 for ; Fri, 19 Feb 2021 16:17:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 35C2464EC0 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.86968.163719 (Exim 4.92) (envelope-from ) id 1lD8Sf-0007Lo-Mx; Fri, 19 Feb 2021 16:16:57 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 86968.163719; Fri, 19 Feb 2021 16:16:57 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD8Sf-0007Lh-Jz; Fri, 19 Feb 2021 16:16:57 +0000 Received: by outflank-mailman (input) for mailman id 86968; Fri, 19 Feb 2021 16:16:56 +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 1lD8Se-0007Lc-Ev for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 16:16:56 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id a12b14bb-5534-4e53-a73a-2a9c777b8bd3; Fri, 19 Feb 2021 16:16:55 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E89E7AC6E; Fri, 19 Feb 2021 16:16:54 +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: a12b14bb-5534-4e53-a73a-2a9c777b8bd3 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=1613751415; 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=tBkMQYeVZQwzEvmOaxxs4K2wmCKetPkqRG4QRy5Q4tw=; b=Sd2O2v66TsNXNIAYSZ/Bbs6qxaJxvAFIOc6Eck9YbUz30UDmYTYtRC+WRk3xbAlxhc+aoH 5t9qEmvLITpdodIoxUxbNOr4wO/CCJs4DPeOfuxHX0McDeprrq43KuZPvEypyht9auH+zS wlPPSc5Hezt4DLFNh/K0m7Ce4A3qMUw= Subject: Re: [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors To: Ian Jackson Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , George Dunlap References: <24623.56913.290437.499946@mariner.uk.xensource.com> <381560e0-e108-c77a-7c43-ae6eb559bba9@suse.com> <24623.58260.98531.223090@mariner.uk.xensource.com> From: Jan Beulich Message-ID: Date: Fri, 19 Feb 2021 17:16:55 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <24623.58260.98531.223090@mariner.uk.xensource.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 19.02.2021 17:13, Ian Jackson wrote: > Jan Beulich writes ("Re: [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors"): >> On 19.02.2021 16:50, Ian Jackson wrote: >>> You say "consistency" but in practical terms, what will happen if the >>> code is not "conxistent" in this sense ? >> >> Patches 4-6: The code is harder to understand with the mix of names. >> Backports from future versions to 4.15 may require more attention to >> get right (and then again the same level of attention when moving to >> 4.14). >> >> Patches 7 is simply a minor improvement. Patch 8 is an equivalent >> of the one patch of the earlier version which has already gone in. >> Just like that other one it's more to avoid a latent issue than any >> active one. > > Thank you for this clear explanation. > > I think 4-6 and 8 are good candidates for the reasons you give, and > because they seem low risk to me. Have you used any automatic > techniques to check that there is no unintentional codegen change ? > (Eg, binary diffs, diffing sedderied versions, or something.) I did some manual inspection at the time of putting together that work, but nothing further to be honest. > To my naive eye patch 7 looks scary because it might be moving the > scope of a critical section. Am I wrong about that ? At the source level it moves things, yes. Generated code, again as per manual inspection, doesn't change, due to the pieces that the compiler is able to eliminate. So I guess it's not as scary as it may look. Jan