FreeBSD 12.1 i386 on Hyper-V Fails to Mount Root

[Wei Hu]

> Howdy,
> 
> Just started the upgrade process on some FreeBSD 11.4 VMs to FreeBSD 12.1
> using freebsd-update. VMs are running on multiple Hyper-V 2012 R2 and 2019
> systems, all systems with 2020-09 Cumulative Updates installed.
> The amd64 VMs are upgrading happily.
> The i386 VMs die a horrible death - the kernel throws the following error:
> 
> vmbus0: cannot find free IDT vector
> 
> shortly followed by mountroot failure due to the lack of storage device
> initialisation.
> Checked the FreeBSD 12.1 i386 ISO in case of environment pollution - same
> vmbus error, same lack of storage device initialisation failure. Ditto with
> the 12.2-RC2 i386 ISO.
> 
Did you try 12.0? Maybe something changed in 12.x causes failure. 
I386 is not well tested on Hyper-V. I will try to reproduce and take a look.

Thanks,
Wei