Possible bug? DOM-U network stopped working after fatal error reported in DOM0

["G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>]

Hi all,

I ran into the following error report in the DOM0 kernel after a recent upgrade:
[  501.840816] vif vif-1-0 vif1.0: Cross page boundary, txp->offset:
2872, size: 1460
[  501.840828] vif vif-1-0 vif1.0: fatal error; disabling device
[  501.841076] xenbr0: port 2(vif1.0) entered disabled state
Once this error happens, the DOM-U behind this vif is no-longer
accessible. And recreating the same DOM-U does not fix the problem.
Only a reboot on the physical host machine helps.

The problem showed up after a recent upgrade on the DOM-U OS from
FreeNAS 11.3 to TrueNAS 12.0U7 and breaks the iSCSI service while
leaving other services like NFS intact.
The underlying OS for the NAS is FreeBSD, version 11.3 and 12.2 respectively.
So far I have tried the following combos:
- Linux 4.19 DOM0 + XEN 4.8 + FreeBSD 11.3 DOM-U: Good
- Linux 4.19 DOM0 + XEN 4.8 + FreeBSD 12.2 DOM-U: Regressed
- Linux 5.10 DOM0 + XEN 4.8 + FreeBSD 12.2 DOM-U: Regressed
- Linux 5.10 DOM0 + XEN 4.11 + FreeBSD 12.2 DOM-U: Regressed

I plan to try out the XEN 4.14 version which is the latest I can get
from the distro (Debian).
If that still does not fix the problem, I would build the 4.16 version
from source as my last resort.

I have to admit that this trial process is blind as I have no idea
which component in the combo is to be blamed. Is it a bug in the
backend-driver, frontend-driver or the hypervisor itself? Or due to
incompatible versions? Any suggestion on other diagnose ideas (e.g.
debug logs) will be welcome, while I work on the planned experiments.

Thanks,
G.R.