s390x: migration to 4.2 makes it unable to migrate back to 4.0
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
Ubuntu on IBM z Systems |
Fix Released
|
High
|
bugproxy | ||
libvirt (Ubuntu) |
Invalid
|
Undecided
|
Unassigned | ||
qemu (Ubuntu) |
Opinion
|
Undecided
|
Unassigned |
Bug Description
Further testing has found more s390x migration issues.
Migration from a former release to the new stack (works) and back (fails).
Lets pick the closest release Eoan as an example.
A guest started on Eoan (libvirt 5.4 qemu 4.0) migrates to Focal (libvirt 6.0 / qemu 4.2) fine.
But on the way back it breaks with:
error: internal error: qemu unexpectedly closed the monitor: 2020-01-
As you know this is a typical scenario on upgrades in case you want to e.g. roll back this issue would break your case.
apqi was added in 4.1 - so that all fits together.
But my expectation from recent years on x86 would have been that on the forward migration the attribute isn't added and then due to that it could properly migrate backward again.
All this seems to be part of the cpu modelling.
- guest is started on source without <cpu ... model>
- migration to the new stack adds <cpu ... model>
- reverse migration is impossible
If I start with host-model on the source then the model stays unmodified and reverse migration works as well.
I know you need proper CPU modelling to make any guarantees, but if the source has none I'd expect the migration not to add one making it impossible to move back.
Please let me know if for you (=for IBM) this is a "oh crap that needs to be fixed" or a "well that is what it is" severity bug?
---
please ignore comment #2 and comment #3 - that is a good case by using host-model on the source.
The data for the bad case is in comment #6
tags: | added: reverse-proxy-bugzilla s390x |
Changed in ubuntu-z-systems: | |
assignee: | nobody → bugproxy (bugproxy) |
importance: | Undecided → High |
status: | New → Triaged |
tags: | added: architecture-s39064 bugnameltc-183536 severity-high targetmilestone-inin2004 |
Host-model as in base template being something like: hvm</type>
<domain type='kvm'>
<os>
<type>
<boot dev='hd'/>
</os>
<cpu mode='host-model'/> <-- here
<devices>
<interface type='network'>
<source network='default'/>
<model type='virtio'/>
</interface>
<console type='pty' tty='/dev/pts/3'>
<source path='/dev/pts/3'/>
<target type='sclp' port='0'/>
<alias name='console0'/>
</console>
</devices>
</domain>