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[188.85.120.92]) by smtp.gmail.com with ESMTPSA id a4-20020adffac4000000b00304ae802f02sm17293776wrs.66.2023.05.10.05.19.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 May 2023 05:19:32 -0700 (PDT) From: Juan Quintela To: Fiona Ebner Cc: QEMU Developers , Peter Xu , leobras@redhat.com, Jonathan.Cameron@huawei.com, dave.jiang@intel.com, fan.ni@samsung.com, "Michael S . Tsirkin" , Thomas Lamprecht Subject: Re: Question about issue #1576: Migration from v8.0.0-rc2 to v7.2.0 with pcie-root-port device fails In-Reply-To: <13090490-af78-042d-dd3e-ca9a45d20bdf@proxmox.com> (Fiona Ebner's message of "Wed, 10 May 2023 11:31:09 +0200") References: <13090490-af78-042d-dd3e-ca9a45d20bdf@proxmox.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) Date: Wed, 10 May 2023 14:19:31 +0200 Message-ID: <87mt2c8jl8.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=170.10.129.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_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: quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Fiona Ebner wrote: > Hi, > I'm trying to fix issue #1576 [0], but having a bit of a hard time. > > The issue was introduced by commit 010746ae1d ("hw/pci/aer: Implement > PCI_ERR_UNCOR_MASK register") and the migration error is: >> qemu-system-x86_64: get_pci_config_device: Bad config data: i=0x10a read: 40 device: 0 cmask: ff wmask: 0 w1cmask:0 > > Since there is no dedicated subsection for the new register, but it's > just part of the existing buffer sent along with the device, the > approach described in docs/devel/migration.rst, "Connecting subsections > to properties" doesn't seem to work here. > > AFAIU, it would be necessary to unset the new register in the buffer > before sending for older machine types (before the patch, its value was > 0). Then older QEMU versions should accept the migration stream again. > Migration between >8.0 and >= 8.0 when using an older machine type would > be softly broken, because the register value is reset to 0, but not be a > hard error, because it's the same situation as forward migration from > 7.2 (the error condition in get_pci_config_device() doesn't trigger, > because versions with commit 010746ae1d set the wmask for the new > register during device initialization). > > Is there a good way to unset the register conditionally based on machine > type during save? Is there any fix for a similar issue in the past I can > look at? > > Or will this be a WONTFIX, because it's just backwards migration and > QEMU 8.0 has already been released? > > [0]: https://gitlab.com/qemu-project/qemu/-/issues/1576 There is a patch on list from Leonardo: https://lists.gnu.org/archive/html/qemu-devel/2023-05/msg00350.html Or I am missing something? Later, Juan.