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 0B507C433DB for ; Fri, 19 Feb 2021 17:05:52 +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 AB81964E57 for ; Fri, 19 Feb 2021 17:05:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB81964E57 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.87006.163868 (Exim 4.92) (envelope-from ) id 1lD9Dk-0005QP-6W; Fri, 19 Feb 2021 17:05:36 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 87006.163868; Fri, 19 Feb 2021 17:05:36 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD9Dk-0005QI-1t; Fri, 19 Feb 2021 17:05:36 +0000 Received: by outflank-mailman (input) for mailman id 87006; Fri, 19 Feb 2021 17:05:35 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD9Di-0005QB-UO for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 17:05:34 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD9Di-0005DG-Rv for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 17:05:34 +0000 Received: from iwj (helo=mariner.uk.xensource.com) by xenbits.xenproject.org with local-bsmtp (Exim 4.92) (envelope-from ) id 1lD9Di-0008Jp-QZ for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 17:05:34 +0000 Received: from iwj by mariner.uk.xensource.com with local (Exim 4.89) (envelope-from ) id 1lD9Df-0001Ty-Ly; Fri, 19 Feb 2021 17:05:31 +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=+EICzCcB8txsTdiA7EvP5djlrzhJs+nXTRVs3jeK/94=; b=0PWmZ8c1AcEk3iU3/sBumcfmwD sYik+Q/bfsPuUjGl4K4VolYKtfnZfzLIy08Qnts2sbNcX+lO2Yu9Wyz0/wcjvvREFjEnowo1c5Isy iTJE5rllXLFvvQwoSZDAce8dVEQCnxkYTNgLtxTU40/qSaKU7m5K441kj0cgRPyf8bzk=; From: Ian Jackson MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <24623.61403.440917.434@mariner.uk.xensource.com> Date: Fri, 19 Feb 2021 17:05:31 +0000 To: Jan Beulich Cc: "xen-devel\@lists.xenproject.org" , Kevin Tian , Julien Grall , Andrew Cooper , Wei Liu , Roger Pau =?iso-8859-1?Q?Monn=E9?= , George Dunlap Subject: Re: [PATCH for-4.15 v2] VMX: use a single, global APIC access page [and 1 more messages] In-Reply-To: , References: X-Mailer: VM 8.2.0b under 24.5.1 (i686-pc-linux-gnu) Jan Beulich writes ("[PATCH v2] VMX: use a single, global APIC access page"): > The address of this page is used by the CPU only to recognize when to > access the virtual APIC page instead. No accesses would ever go to this > page. It only needs to be present in the (CPU) page tables so that > address translation will produce its address as result for respective > accesses. > > By making this page global, we also eliminate the need to refcount it, > or to assign it to any domain in the first place. Thanks for this. >From this: Jan Beulich writes ("Re: [PATCH v2] VMX: use a single, global APIC access page"): > While this patch was triggered not just by Julien's observation of > the early p2m insertion being a problem, but also many earlier > times of running into this odd code, it is - especially at this > stage - perhaps a possible option to split the change into just > the movement of the set_mmio_p2m_entry() invocation and all the > rest, in order to defer that rest until after 4.15. I infer that this contains a bugfix, but perhaps other changes/improvements too. George, I think you're our expert on this refcounting stuff - what do you think of this ? I guess my key question is whether this change will introduce risk by messing with the complex refcounting machineryt - or remove it by removing an interaction with the refcounting. Thanks, Ian.