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=-5.5 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 CB60BC43461 for ; Fri, 4 Sep 2020 16:00:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FB0E20722 for ; Fri, 4 Sep 2020 16:00:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726771AbgIDQAP (ORCPT ); Fri, 4 Sep 2020 12:00:15 -0400 Received: from mga01.intel.com ([192.55.52.88]:29411 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726127AbgIDQAO (ORCPT ); Fri, 4 Sep 2020 12:00:14 -0400 IronPort-SDR: p8h0t8mTpBiLdWIa0lCT2hDK/9FmG8zdObq84BgZqMShFEzbEdvKJB6rV0qY74DXuFdaq8iLDI jGaF/agi6LbQ== X-IronPort-AV: E=McAfee;i="6000,8403,9734"; a="175822319" X-IronPort-AV: E=Sophos;i="5.76,390,1592895600"; d="scan'208";a="175822319" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Sep 2020 09:00:12 -0700 IronPort-SDR: B0zfEkIxhDFm2q4frTASRz7FOgl7CEHz9Q72W6CC3ioa5Lv3Tv2kK5vDrwxBrX/5AQR4oq9jq0 7vT+c1KM7zlg== X-IronPort-AV: E=Sophos;i="5.76,390,1592895600"; d="scan'208";a="478552197" Received: from sjchrist-ice.jf.intel.com (HELO sjchrist-ice) ([10.54.31.34]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Sep 2020 09:00:12 -0700 Date: Fri, 4 Sep 2020 09:00:10 -0700 From: Sean Christopherson To: Gerd Hoffmann Cc: Vitaly Kuznetsov , Peter Xu , kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , Michael Tsirkin , Julia Suvorova , Andy Lutomirski , Andrew Jones , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory Message-ID: <20200904160008.GA2206@sjchrist-ice> References: <20200807141232.402895-1-vkuznets@redhat.com> <20200825212526.GC8235@xz-x1> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200904072905.vbkiq3h762fyzds6@sirius.home.kraxel.org> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 04, 2020 at 09:29:05AM +0200, Gerd Hoffmann wrote: > Hi, > > > Unless I'm mistaken, microvm doesn't even support PCI, does it? > > Correct, no pci support right now. > > We could probably wire up ecam (arm/virt style) for pcie support, once > the acpi support for mictovm finally landed (we need acpi for that > because otherwise the kernel wouldn't find the pcie bus). > > Question is whenever there is a good reason to do so. Why would someone > prefer microvm with pcie support over q35? > > > If all of the above is true, this can be handled by adding "pci=lastbus=0" > > as a guest kernel param to override its scanning of buses. And couldn't > > that be done by QEMU's microvm_fix_kernel_cmdline() to make it transparent > > to the end user? > > microvm_fix_kernel_cmdline() is a hack, not a solution. > > Beside that I doubt this has much of an effect on microvm because > it doesn't support pcie in the first place. I am so confused. Vitaly, can you clarify exactly what QEMU VM type this series is intended to help? If this is for microvm, then why is the guest doing PCI scanning in the first place? If it's for q35, why is the justification for microvm-like workloads? Either way, I think it makes sense explore other options before throwing something into KVM, e.g. modifying guest command line, adding a KVM hint, "fixing" QEMU, etc...