Bhyve Broken: whose fault (AMD, FreeBSD, ZFS ...?)

[Zaphod Beeblebrox]

Since I found out that I can't run a Samba directory server in a jail, I've
had the setup of a bhyve on my list.  I had toyed with Bhyve 6 or 8 months
ago, and still had the images, so I zfs cloned one and set about a source
upgrade.

This ignomineously hung.

So... I upgraded the host to 11.1-RC3, and I reinstalled a fresh guest from
the 11.1-RC3 install CD.  The guest uses UFS2 on a 40G disk, the server is
an AMD 9590 with 32G RAM and a 40T ZFS array.

After installation, I started the guest again with 1G ram, 4 processors (of
the 8 on the source CPU) and tried a buildworld again.  This time the guest
crashed and rebooted.

What should be next steps here?  This is repeatable.  The host is stable
(it can makeworld -j32 in about 25 minutes ... so it's hardware seems
good).  Is this an AMD bug?  Is it bad to use ZFS ZVols?