Re: Guest migration between different Ryzen CPU generations

[Paolo Bonzini <pbonzini@redhat.com>]

On 5/31/22 19:00, mike tancsa wrote:
> 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.
Hi, this is probably related to the patch at 
https://www.spinics.net/lists/stable/msg538630.html, which needs a 
backport to 5.15 however.

Note that using Intel definitions on AMD or vice versa is not going to 
always work, though in this case it seems to be a regression.

Paolo