On Tue, 31 May 2022 13:00:07 -0400 mike tancsa <mike@xxxxxxxxxx> wrote: > Hello, > > I have been using kvm since the Ubuntu 18 and 20.x LTS series of > kernels and distributions without any issues on a whole range of Guests > up until now. Recently, we spun up an Ubuntu LTS 22 hypervisor to add to > the mix and eventually upgrade to. Hardware is a series of Ryzen 7 CPUs > (3700x). Migrations back and forth without issue for Ubuntu 20.x > kernels. The first Ubuntu 22 machine was on identical hardware and all > was good with that too. The second Ubuntu 22 based machine was spun up > with a newer gen Ryzen, a 5800x. On the initial kernel version that > came with that release back in April, migrations worked as expected > between hardware as well as different kernel versions and qemu / KVM > versions that come default with the distribution. Not sure if migrations > between kernel and KVM versions "accidentally" worked all these years, > but they did. However, we ran into an issue with the kernel > 5.15.0-33-generic (possibly with 5.15.0-30 as well) thats part of > Ubuntu. Migrations no longer worked to older generation CPUs. I could > send a guest TO the box and all was fine, but upon sending the guest to > another hypervisor, the sender would see it as successfully migrated, > but the VM would typically just hang, with 100% CPU utilization, or > sometimes crash. I tried a 5.18 kernel from May 22nd and again the > behavior is different. If I specify the CPU as EPYC or EPYC-IBPB, I can > migrate back and forth. perhaps you are hitting issue fixed by: https://lore.kernel.org/lkml/CAJ6HWG66HZ7raAa+YK0UOGLF+4O3JnzbZ+a-0j8GNixOhLk9dA@xxxxxxxxxxxxxx/T/ > Quick summary > > On Ubuntu 20.04 LTS with latest Ubuntu updates, I can migrate VMs back > and forth between a 3700x and a 5800x without issue. Guests are a mix of > Ubuntu, Fedora and FreeBSD > On Ubuntu 22 LTS, with the original kernel from release day, I can > migrate VMs back and forth between a 3700x and a 5800x without issue > On Ubuntu 22 LTS with everything up to date as of mid May 2022, I can > migrate from the 3700X to the 5800x without issue. But going from the > 5800x to the 3700x results in a migrated VM that either crashes inside > the VM or has the CPU pegged at 100% spinning its wheels with the guest > frozen and needing a hard reset. This is with --live or without and with > --unsafe or without. The crash / hang happens once the VM is fully > migrated with the sender thinking it was successfully sent and the > receiver thinking it successfully arrived in. > On stock Ubuntu 22 (5.15.0-33-generic) I can migrate back and forth to > Ubuntu 20 as long as the hardware / cpu is identical (in this case, 3700x) > On Ubuntu 22 LTS with everything up to date as of mid May 2022 with > 5.18.0-051800-generic #202205222030 SMP PREEMPT_DYNAMIC Sun May 22. I > can migrate VMs back and forth that have as its CPU def EPYC or > EPYC-IBPB. If the def (in my one test case anyways) is Nehalem then I > get a frozen VM on migration back to the 3700X. > > Some more details at > > https://ubuntuforums.org/showthread.php?t=2475399 > > Is this a bug ? Expected behavior ? Is there a better place to ask > these questions ? > > Thanks in advance! > > ---Mike >
