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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB413C433F5 for ; Wed, 29 Sep 2021 09:07:24 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 48E33613A7 for ; Wed, 29 Sep 2021 09:07:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 48E33613A7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:46562 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mVVYh-0004iK-1v for qemu-devel@archiver.kernel.org; Wed, 29 Sep 2021 05:07:23 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39774) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mVVWz-0003oC-5Q for qemu-devel@nongnu.org; Wed, 29 Sep 2021 05:05:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:24215) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mVVWt-0002tg-NQ for qemu-devel@nongnu.org; Wed, 29 Sep 2021 05:05:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632906330; h=from:from:reply-to:reply-to:subject:subject: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=wPoLJq8hH9MSD5a1S7FVEKq+yn/SA3XBMYU++5jfFVU=; b=Mf5TwsuEaZfZaQ1gyyzQsonfFuVVGPK2CqfGousrXYtdOQXkwFjadjBDwvinez5tu5kc+C rRl0tg1i5U3vDA4500e19HCWhYHeL66yNPRR0ZgdtwGOraKzL5v8y667DRviSZhNE/lXvh gfpd9B5Wx+4unsM68QANu+XiBJ6sC5o= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-518-s-L4HcWVPGuHXqn4ypzHrw-1; Wed, 29 Sep 2021 05:05:24 -0400 X-MC-Unique: s-L4HcWVPGuHXqn4ypzHrw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B08E5652; Wed, 29 Sep 2021 09:05:23 +0000 (UTC) Received: from redhat.com (unknown [10.39.192.82]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E98A45E7A2; Wed, 29 Sep 2021 09:05:14 +0000 (UTC) Date: Wed, 29 Sep 2021 10:05:11 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Michael S. Tsirkin" Subject: Re: [PULL 1/5] hw/pcie-root-port: Fix hotplug for PCI devices requiring IO Message-ID: References: <20210803205043.165034-1-mst@redhat.com> <20210803205043.165034-2-mst@redhat.com> <20210927053932-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20210927053932-mutt-send-email-mst@kernel.org> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Marcel Apfelbaum , Peter Maydell , qemu-devel@nongnu.org, Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Sep 27, 2021 at 05:49:15AM -0400, Michael S. Tsirkin wrote: > On Mon, Sep 27, 2021 at 10:33:42AM +0100, Daniel P. Berrangé wrote: > > On Tue, Aug 03, 2021 at 04:52:03PM -0400, Michael S. Tsirkin wrote: > > > From: Marcel Apfelbaum > > > > > > Q35 has now ACPI hotplug enabled by default for PCI(e) devices. > > > As opposed to native PCIe hotplug, guests like Fedora 34 > > > will not assign IO range to pcie-root-ports not supporting > > > native hotplug, resulting into a regression. > > > > > > Reproduce by: > > > qemu-bin -M q35 -device pcie-root-port,id=p1 -monitor stdio > > > device_add e1000,bus=p1 > > > In the Guest OS the respective pcie-root-port will have the IO range > > > disabled. > > > > > > Fix it by setting the "reserve-io" hint capability of the > > > pcie-root-ports so the firmware will allocate the IO range instead. > > > > > > Acked-by: Igor Mammedov > > > Signed-off-by: Marcel Apfelbaum > > > Message-Id: <20210802090057.1709775-1-marcel@redhat.com> > > > Reviewed-by: Michael S. Tsirkin > > > Signed-off-by: Michael S. Tsirkin > > > --- > > > hw/pci-bridge/gen_pcie_root_port.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > This change, when combined with the switch to ACPI based hotplug by > > default, is responsible for a significant regression in QEMU 6.1.0 > > > > It is no longer possible to have more than 15 pcie-root-port devices > > added to a q35 VM in 6.1.0. Before this I've had as many as 80+ devices > > present before I stopped trying to add more. > > > > https://gitlab.com/qemu-project/qemu/-/issues/641 > > > > This regression is significant, because it has broken the out of the > > box default configuration that OpenStack uses for booting all VMs. > > They add 16 pcie-root-ports by defalt to allow empty slots for device > > hotplug under q35 [1]. > > > Indeed, oops. Thanks for the report! > > Going back and looking at seabios code, didn't we get confused? > Shouldn't we have reserved memory and not IO? > > I see: > int resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO); > if (!sum && hotplug_support && !resource_optional) > sum = align; /* reserve min size for hot-plug */ > > > generally maybe we should just add an ACPI-hotplug capability and > teach seabios about it? Looking at the commit message example: qemu-bin -M q35 -device pcie-root-port,id=p1 -monitor stdio device_add e1000,bus=p1 IIUC, that is plugging a PCI device into the PCIe root port. docs/pcie.txt says that IO space is not allocated by SeaBIOS or OVMF for pcie-root-port, if (1) the port is empty, or (2) the device behind the port has no IO BARs. Point (2) is satisified if you only ever plug PCIe devces into the pcie-root-port. The docs/pcie.txt recommends exactly that, with any PCI device to be placed downstream of a pcie-pci-bridge and pci-pci-bridge pair. IOW that example from the commit message should have been qemu-bin -M q35 -device pcie-root-port,id=p1 -monitor stdio \ -device pcie-pci-bridge,id=br1,bus=pcie.0] \ -device pci-bridge,id=br2,bus=br1,chassis_nr=1 device-add e1000,bus=br2 So why did we need IO space for the pcie-root-port at all ? The example given as the reason just looks like user error per the docs/pcie.txt Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|