Michael Tokarev <m...@tls.msk.ru> wrote: > 11.05.2023 11:40, Juan Quintela wrote: >> Fiona Ebner <f.eb...@proxmox.com> wrote: > ... >>> Closes: https://gitlab.com/qemu-project/qemu/-/issues/1576 >>> >>> AFAICT, this breaks (forward) migration from 8.0 to 8.0 + this patch >>> when using machine type <= 7.2. That is because after this patch, when >>> using machine type <= 7.2, the wmask for the register is not set and >>> when 8.0 sends a nonzero value for the register, the error condition in >>> get_pci_config_device() will trigger again. >> I think that works correctly. >> See https://lists.gnu.org/archive/html/qemu-devel/2023-05/msg02733.html >> What we have (before this patch) (using abbrevs as in the doc >> before) >> Current state: >> (1) qemu-8.0 -M pc-8.0 -> qemu-8.0 -M pc-8.0 works >> not affected by the patch >> (2) qemu-7.2 -M pc-7.2 -> qemu-8.0 -M pc-8.0 works >> works well because 7.2 don't change that field >> (3) qemu-8.0 -M pc-7.2 -> qemu-7.2 -M pc-7.2 fails >> With the patch we fixed 3, so once it is in stable, 1 and 2 continue >> as >> usual and for (3) we will have: >> (3) qemu-8.0.1 -M pc-7.2 -> qemu-7.2 -M pc-7.2 works >> If what you mean is that: >> (3) qemu-8.0 -M pc-7.2 -> qemu-8.0.1 -M pc-7.2 works >> Will fail, that is true, but I can think a "sane" way to fix this.
Hi > That's a great summary indeed. Thanks. >>> Is it necessary to also handle that? Maybe by special casing the error >>> condition in get_pci_config_device() to be prepared to accept such a >>> stream from 8.0? >> Well, we can do that, but it is to the pci maintainers to decide if >> that >> is "sane". > > So, can we go from here somewhere? I'd love this fix to be in 8.0.1, > either with or without the (un)sane part of the (3) variant above which > might fail. Or else we'll have the same situation in 8.0.1 as we now > have in 8.0.0 (the deadline is May-27). > > We did broke x.y.0 => x.y.1 migration before already like this, such as > with 7.2.0=>7.2.1. I'm not saying it's a nice thing to do, just stating > a fact. Yes, it is better to avoid such breakage, but.. meh.. See patch for documentation: https://lists.gnu.org/archive/html/qemu-devel/2023-05/msg03288.html Basically, the best we can do is: - get the patch posted. Fixes everything except: (3) qemu-8.0 -M pc-7.2 -> qemu-8.0.1 -M pc-7.2 works And for that, we can document somewhere that we need to launch qemu-8.0.1 as: $ qemu-8.0.1 -M pc-7.2 -device blah,x-pci-err-unc-mask=on And mark someone that this machine is tainted an can only be migrated to qemu's >= qemu-8.0.1. And that we should reboot it as the user convenience. (reboot here means poweroff qemu and poweron it back without x-pci-err-unc-mask=on). Later, Juan.
