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 39AC7C77B7A for ; Wed, 17 May 2023 07:10:54 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pzBIZ-0007wK-Ds; Wed, 17 May 2023 03:10:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pzBIT-0007vx-Vw for qemu-devel@nongnu.org; Wed, 17 May 2023 03:10:06 -0400 Received: from proxmox-new.maurer-it.com ([94.136.29.106]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pzBIQ-00073g-7w for qemu-devel@nongnu.org; Wed, 17 May 2023 03:10:05 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 1E630453DA; Wed, 17 May 2023 09:09:48 +0200 (CEST) Message-ID: <42862ba2-4c46-f8a7-66fb-1d56104d64af@proxmox.com> Date: Wed, 17 May 2023 09:09:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v3 3/3] migration/doc: We broke backwards compatibility To: Juan Quintela , qemu-devel@nongnu.org Cc: "Michael S . Tsirkin" , Leonardo Bras , Peter Xu , Jiri Denemark , Avihai Horon , =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= References: <20230515083201.55060-1-quintela@redhat.com> <20230515083201.55060-4-quintela@redhat.com> Content-Language: en-US From: Fiona Ebner In-Reply-To: <20230515083201.55060-4-quintela@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=94.136.29.106; envelope-from=f.ebner@proxmox.com; helo=proxmox-new.maurer-it.com X-Spam_score_int: -45 X-Spam_score: -4.6 X-Spam_bar: ---- X-Spam_report: (-4.6 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-2.666, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 15.05.23 um 10:32 schrieb Juan Quintela: > When we detect that we have broken backwards compantibility in a compatibility (...) > + > +In qemu-8.0 we got this commit: :: > + > + commit 9a6ef182c03eaa138bae553f0fbb5a123bef9a53 > + Author: Jonathan Cameron > + Date: Thu Mar 2 13:37:03 2023 +0000 > + > + hw/pci/aer: Add missing routing for AER errors > + > +The relevant bits of the commit for our example are this ones: > + > + --- a/hw/pci/pcie_aer.c > + +++ b/hw/pci/pcie_aer.c > + @@ -112,6 +112,10 @@ int pcie_aer_init(PCIDevice *dev, > + > + pci_set_long(dev->w1cmask + offset + PCI_ERR_UNCOR_STATUS, > + PCI_ERR_UNC_SUPPORTED); > + + pci_set_long(dev->config + offset + PCI_ERR_UNCOR_MASK, > + + PCI_ERR_UNC_MASK_DEFAULT); > + + pci_set_long(dev->wmask + offset + PCI_ERR_UNCOR_MASK, > + + PCI_ERR_UNC_SUPPORTED); > + > + pci_set_long(dev->config + offset + PCI_ERR_UNCOR_SEVER, > + PCI_ERR_UNC_SEVERITY_DEFAULT); > + These changes are not part of commit 9a6ef182c0 ("hw/pci/aer: Add missing routing for AER errors") but rather the one before it, namely 010746ae1d ("hw/pci/aer: Implement PCI_ERR_UNCOR_MASK register") > +The patch changes how we configure pci space for AER. But qemu fails Should QEMU and PCI be capitalized in the text parts? > +when the pci space configuration is different betwwen source and between > +destination. > + > +The following commit show how this got fixed: shows (...) > + > +So the normality has been restaured and everything is ok, no? restored > + > +Not really, now our matrix is much bigger. We started with the easy > +cases, migration from the same version to the same version always > +works: > + > +- $ qemu-7.2 -M pc-7.2 -> qemu-7.2 -M pc-7.2 > +- $ qemu-8.0 -M pc-7.2 -> qemu-8.0 -M pc-7.2 > +- $ qemu-8.0.1 -M pc-7.2 -> qemu-8.0.1 -M pc-7.2 > + > +Now the interesting ones. When the QEMU processes versions are > +different. For the 1st set, their fail and we can do nothing, both > +versions are relased and we can't change anything. released > + > +- $ qemu-7.2 -M pc-7.2 -> qemu-8.0 -M pc-7.2 > +- $ qemu-8.0 -M pc-7.2 -> qemu-7.2 -M pc-7.2 > + > +This two are the ones that work. The whole point of making the > +change in qemu-8.0.1 release was to fix this issue: > + > +- $ qemu-7.2 -M pc-7.2 -> qemu-8.0.1 -M pc-7.2 > +- $ qemu-8.0.1 -M pc-7.2 -> qemu-7.2 -M pc-7.2 > + > +But now we found that qemu-8.0 neither can migrate to qemu-7.2 not > +qemu-8.0.1. > + > +- $ qemu-8.0 -M pc-7.2 -> qemu-8.0.1 -M pc-7.2 > +- $ qemu-8.0.1 -M pc-7.2 -> qemu-8.0 -M pc-7.2 > + > +So, if we start a pc-7.2 machine in qemu-8.0 we can't migrate it to > +anything except to qemu-8.0. > + > +Can we do better? > + > +Yeap. If we know that we are gonig to do this migration: going > + > +- $ qemu-8.0 -M pc-7.2 -> qemu-8.0.1 -M pc-7.2 > + > +We can launche the appropiate devices with "launch" was already pointed out by Peter, but there's also "appropriate" > + > +--device...,x-pci-e-err-unc-mask=on > + > +And now we can receive a migration from 8.0. And from now on, we can > +do that migration to new machine types if we remember to enable that > +property for pc-7.2. Notice that we need to remember, it is not > +enough to know that the source of the migration is qemu-8.0. Think of this example: > + > +$ qemu-8.0 -M pc-7.2 -> qemu-8.0.1 -M pc-7.2 -> qemu-8.2 -M pc-7.2 > + > +In the second migration, the source is not qemu-8.0, but we still have > +that "problem" and have that property enabled. Notice that we need to > +continue having this mark/property until we have this machine > +rebooted. But it is not a normal reboot (that don't reload qemu) we > +need the mapchine to poweroff/poweron on a fixed qemu. And from now machine Best Regards, Fiona