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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id EFD5CC433EF for ; Wed, 20 Jul 2022 11:06:14 +0000 (UTC) Received: from localhost ([::1]:47552 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oE7Wv-0006bh-JQ for qemu-devel@archiver.kernel.org; Wed, 20 Jul 2022 07:06:14 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55896) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oE7W0-0005tf-JA for qemu-devel@nongnu.org; Wed, 20 Jul 2022 07:05:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:48408) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oE7Vx-0005ng-8Y for qemu-devel@nongnu.org; Wed, 20 Jul 2022 07:05:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1658315112; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CrGB2GYqPrFqmCIqeCqe2CtZ0UQ1ZDy47874LHaFdKo=; b=hy5FgGuYkgcVaPoqmWD5FcKsbotCMigpCUV/NJQZPmaX6xbbtaWXqVh4hzZOjECfETIg01 SExOfxLJRDr/sDkcO/SujMN3/y/tNq5FIhme6ZS1RFYMrLpMnckwMxoqg77b9TLboUeWtF OIG0EWLi6CWJPhKqoOgD49jjyjrRZJ4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-298-UkM0ikq3PPW8kkRKPWB_0Q-1; Wed, 20 Jul 2022 07:05:02 -0400 X-MC-Unique: UkM0ikq3PPW8kkRKPWB_0Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 85C24185A7B2; Wed, 20 Jul 2022 11:05:02 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EF83FC15D67; Wed, 20 Jul 2022 11:05:00 +0000 (UTC) Date: Wed, 20 Jul 2022 12:04:58 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Roman Kagan , qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy , Thomas Huth , Laurent Vivier , Marcel Apfelbaum , yc-core@yandex-team.ru, Paolo Bonzini , "Michael S. Tsirkin" Subject: Re: [PATCH v3] hw/pci/pci_bridge: ensure PCIe slots have only one slot Message-ID: References: <20220720102555.874394-1-rvkagan@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.6 (2022-06-05) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 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: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 20, 2022 at 02:00:16PM +0300, Roman Kagan wrote: > On Wed, Jul 20, 2022 at 11:44:26AM +0100, Daniel P. Berrangé wrote: > > On Wed, Jul 20, 2022 at 01:25:55PM +0300, Roman Kagan wrote: > > > It's possible to create non-working configurations by attaching a device > > > to a derivative of PCIe slot (pcie-root-port, ioh3420, etc) and > > > specifying a slot number other that zero, e.g.: > > > > > > -device pcie-root-port,id=s0,... \ > > > -device virtio-blk-pci,bus=s0,addr=4,... > > > > > > Make QEMU reject such configurations and only allow addr=0 on the > > > secondary bus of a PCIe slot. > > > > What do you mean by 'non-working' in this case. The guest OS boots > > OK, but I indeed don't see the device in the guest, but IIUC it was > > said that was just because Linux doesn't scan for a non-zero slot. > > Right. I don't remember if it was Linux or firmware or both but indeed > at least Linux guests don't see devices if attached to a PCIe slot at > addr != 0. (Which is kinda natural for a thing called "slot", isn't it?) I vaguely recall there was an option to tell linux to scan all slots, not just slot 0, not sure if that's applicable here. > > > That wouldn't be a broken config from QEMU's POV though, merely a > > guest OS limitation ? > > Strictly speaking it wouldn't, indeed. But we've had created such a > configuration (due to a bug in our management layer) and spent > non-negligible time trying to figure out why the attached device didn't > appear in the guest. So I thought it made sense to reject a > configuration which is known to confuse guests. Doesn't it? If a configuration is a permissible per the hardware design / spec, then QEMU should generally allow it. We don't want to constrain host side configs based on the current limitations of guest OS whose behaviour can change over time, or where a different guest OS may have a different POV. With 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 :|