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 7D505C433DB for ; Fri, 19 Feb 2021 16:13:21 +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 3F08A64E76 for ; Fri, 19 Feb 2021 16:13:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F08A64E76 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.86964.163708 (Exim 4.92) (envelope-from ) id 1lD8P3-0007Ad-68; Fri, 19 Feb 2021 16:13:13 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 86964.163708; Fri, 19 Feb 2021 16:13:13 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD8P3-0007AV-36; Fri, 19 Feb 2021 16:13:13 +0000 Received: by outflank-mailman (input) for mailman id 86964; Fri, 19 Feb 2021 16:13:11 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD8P1-0007AN-LE for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 16:13:11 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD8P1-0004H2-JA for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 16:13:11 +0000 Received: from iwj (helo=mariner.uk.xensource.com) by xenbits.xenproject.org with local-bsmtp (Exim 4.92) (envelope-from ) id 1lD8P1-0008PJ-Hs for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 16:13:11 +0000 Received: from iwj by mariner.uk.xensource.com with local (Exim 4.89) (envelope-from ) id 1lD8Oy-0001Hz-A6; Fri, 19 Feb 2021 16:13:08 +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=WxeqxFuHJbqY6zzQggWwRIr+agzwPbNQklTmSllrMsc=; b=4hfFgGcARyqSy9L+C2gcTkFp/M 4NiqSAI4qxatzMY1IqkrhPq06fm5qAMQc+njIY7nvqCKOlBsc7Akdy7nvPFJU1fbXOLYOzFuLBaZt a4Ah/qEKsJWEIyyGYZLFMbbJP9TQL8usp+9eaeBCVkwsDld9XY98JF7snnaNbW13JRto=; From: Ian Jackson MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <24623.58260.98531.223090@mariner.uk.xensource.com> Date: Fri, 19 Feb 2021 16:13:08 +0000 To: Jan Beulich Cc: "xen-devel\@lists.xenproject.org" , Andrew Cooper , Wei Liu , Roger Pau =?iso-8859-1?Q?Monn=E9?= , George Dunlap Subject: Re: [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors In-Reply-To: <381560e0-e108-c77a-7c43-ae6eb559bba9@suse.com> References: <24623.56913.290437.499946@mariner.uk.xensource.com> <381560e0-e108-c77a-7c43-ae6eb559bba9@suse.com> X-Mailer: VM 8.2.0b under 24.5.1 (i686-pc-linux-gnu) 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.) To my naive eye patch 7 looks scary because it might be moving the scope of a critical section. Am I wrong about that ? Ian.