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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 28363C43465 for ; Mon, 21 Sep 2020 17:21:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E506D20BED for ; Mon, 21 Sep 2020 17:21:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727665AbgIURVS (ORCPT ); Mon, 21 Sep 2020 13:21:18 -0400 Received: from mga03.intel.com ([134.134.136.65]:47536 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726818AbgIURVS (ORCPT ); Mon, 21 Sep 2020 13:21:18 -0400 IronPort-SDR: Rpb66G1XP4cFtnOcTQKyfoQOQ5T6dMphRist8x4Ncr51tlYZjAHJKheGC9ODnMXVhQCj1TS8zm kQ3cqCoaHppA== X-IronPort-AV: E=McAfee;i="6000,8403,9751"; a="160505400" X-IronPort-AV: E=Sophos;i="5.77,287,1596524400"; d="scan'208";a="160505400" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2020 10:21:17 -0700 IronPort-SDR: VY7pyBgmT7sxVYCPzS3B8Hf7CmR/TndJJxV5G8TYir6MY8UbzeWwFmv0bs7O1+1ZIvP+hp6bJk lE3+0krGJxbA== X-IronPort-AV: E=Sophos;i="5.77,287,1596524400"; d="scan'208";a="510811785" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.160]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2020 10:21:16 -0700 Date: Mon, 21 Sep 2020 10:21:14 -0700 From: Sean Christopherson To: "Michael S. Tsirkin" Cc: Vitaly Kuznetsov , Peter Xu , kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , Julia Suvorova , Andy Lutomirski , Andrew Jones , linux-kernel@vger.kernel.org, Gerd Hoffmann Subject: Re: [PATCH v2 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory Message-ID: <20200921172114.GA24289@linux.intel.com> References: <87eenlwoaa.fsf@vitty.brq.redhat.com> <20200901200021.GB3053@xz-x1> <877dtcpn9z.fsf@vitty.brq.redhat.com> <20200904061210.GA22435@sjchrist-ice> <20200904072905.vbkiq3h762fyzds6@sirius.home.kraxel.org> <20200904160008.GA2206@sjchrist-ice> <874koanfsc.fsf@vitty.brq.redhat.com> <20200907072829-mutt-send-email-mst@kernel.org> <20200911170031.GD4344@sjchrist-ice> <20200918083134-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200918083134-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Sep 18, 2020 at 08:34:37AM -0400, Michael S. Tsirkin wrote: > On Fri, Sep 11, 2020 at 10:00:31AM -0700, Sean Christopherson wrote: > > On Mon, Sep 07, 2020 at 07:32:23AM -0400, Michael S. Tsirkin wrote: > > > I suspect microvms will need pci eventually. I would much rather KVM > > > had an exit-less discovery mechanism in place by then because > > > learning from history if it doesn't they will do some kind of > > > hack on the kernel command line, and everyone will be stuck > > > supporting that for years ... > > > > Is it not an option for the VMM to "accurately" enumerate the number of buses? > > E.g. if the VMM has devices on only bus 0, then enumerate that there is one > > bus so that the guest doesn't try and probe devices that can't possibly exist. > > Or is that completely non-sensical and/or violate PCIe spec? > > > There is some tension here, in that one way to make guest boot faster > is to defer hotplug of devices until after it booted. Sorry, I didn't follow that, probably because my PCI knowledge is lacking. What does device hotplug have to do with the number of buses enumerated to the guest?