Bhyve Exited to UEFI Shell

I have a FreeNAS host where I run a few Bhyve virtual machine (VM) instances. Upon upgrading FreeNAS, I found some VMs did not boot successfully. It turns out that the VMs exited to UEFI Shell, and complained that it could not locate some efi file. The solution that works for me is discussed in this post.

To summarize, I followed the two steps procedure as described in the post:

1. Boot the VM into the guest operating system, in my case, CentOS 7, by (1) exiting the UEFI shell, (2) entering UEFI "Boot Maintenance Manager"; (3) choosing "Boot From File", and (4) browsing the directory and locating grubx64.efi under the folder named after the operating system, in my case, centos/grubx64.efi
2. Copy the efi file to BOOT/BOOTX64.EFI