Failed to restore domain - error load load virtio-balloon:virtio

I noticed a domain restore error on my virtual machines.
I can't reproduce the error on a test virtual machine.

sudo virsh save linux2020 /var/lib/libvirt/qemu/save/linux2020.save
Domain 'linux2020' saved to /var/lib/libvirt/qemu/save/linux2020.save

sudo virsh restore /var/lib/libvirt/qemu/save/linux2020.save
error: Failed to restore domain from /var/lib/libvirt/qemu/save/linux2020.save
error: внутренняя ошибка: QEMU неожиданно завершил работу монитора: qemu-system-x86_64: -chardev socket,id=charchannel0,fd=52,server,nowait: warning: short-form boolean option 'server' deprecated
Please use server=on instead
qemu-system-x86_64: -chardev socket,id=charchannel0,fd=52,server,nowait: warning: short-form boolean option 'nowait' deprecated
Please use wait=off instead
qemu-system-x86_64: -spice port=5900,addr=0.0.0.0,disable-ticketing,image-compression=off,seamless-migration=on: warning: short-form boolean option 'disable-ticketing' deprecated
Please use disable-ticketing=on instead
2021-04-16T09:47:15.037700Z qemu-system-x86_64: VQ 0 size 0x80 < last_avail_idx 0x0 - used_idx 0xcccc
2021-04-16T09:47:15.037737Z qemu-system-x86_64: Failed to load virtio-balloon:virtio
2021-04-16T09:47:15.037744Z qemu-system-x86_64: error while loading state for instance 0x0 of device '0000:00:02.0/virtio-balloon'
2021-04-16T09:47:15.037849Z qemu-system-x86_64: load of migration failed: Operation not permitted

If in the machine configuration replace
<type arch="x86_64" machine="pc-i440fx-5.1">hvm</type>
to
<type arch="x86_64" machine="pc-i440fx-5.0">hvm</type>
the virtual machine is recovering normally



Can you just clarify:
  a) Which version of qemu are you running?
  b) Was the save done with the pc-i440fx-5.1 as well as the load?
  c) What guest are you running?

a) Checked for versions 5.2.0 and 6.0.0rc.
b) Save and restore with pc-i440fx-5.1.
c) Used OS Linux NixOS Unstable.
If clean install NixOS system - the error is not reproduced. It was not possible to track what affects the restore domain.

The QEMU project is currently moving its bug tracking to another system.
For this we need to know how to transfer the bug to the new system if
(if still necessary). Thus we're setting the status to "Incomplete" now.

In the unlikely case that the bug has already been fixed in the final
6.0 release version of QEMU, then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here should be
moved to the new system, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes
anymore).

Thank you and sorry for the inconvenience.


[Expired for QEMU because there has been no activity for 60 days.]

Ticket has been re-opened here :
https://gitlab.com/qemu-project/qemu/-/issues/485