Host system crash - bhyve pci passthrough

I'm running FreeBSD 14.3-RELEASE-p6 on a Supermicro H11SSL motherboard 
with an EPYC 7551 32-core CPU.

This system runs 2 guests under bhyve, both with pci passthough:

 1. A FreeBSD system running off of a physical disk
    (disk0_name="/dev/ada1", disk0_dev="custom") and 2 LSI HBAs passed
    through with pci passthrough for large amounts of storage.
 2. A Linux system running off a zvol on the host with a Google Coral
    Edge TPU passed through.

VM #2 streams approximately 10MiB/s across the virtual network to VM #1 
for storage over NFS.


With the default FreeBSD settings, the host will lock within a couple of 
minutes after VM #2 boots (and sometimes during the Linux boot phase).  
A error that appears on the console is:

swap_pager: indefinite wait buffer: bufobj: 0, blkno: 23943, size: 
28672  (the blkno and size change of course)

When this happens, the system is completely unresponsive, and the Linux 
VM is locked as well.  Sometimes I can bring it back by shutting down VM 
#1 which usually remains responsive for a while, but eventually it will 
also freeze.

Without PCI passthrough, there is no crash.


I've tried many things, but one config element that does seem to delay 
(for up to several days) the freeze has been setting 
vfs.zfs.vdev.max_active=600 in /boot/loader.conf.

Memory usage remains low before a lockup, a tiny fraction of swap is 
used, iostat doesn't show unusual volume, and there's plenty of idle CPU.

I'd love to be able to identify what's actually happening so that I 
could either address it via config changes or to file a defect, but I'm 
unable to find any metrics that are increasing, or any other way to 
trace the issue.

Does anyone either have an idea about what's going on, or know some 
relevant metrics/traces that would help in IDing the issue?

Thanks in advance,


Joseph