Upgrade 4.2 --> 4.3: Documentation of difficulties (`vm-pool` needing manual intervention) and lingering `salt` issues (`ext_pillar interfaces unavailable`)

[stage3help]

@balin1 Is the LVM error you saw the same as this:

4.3 upgrade Error: Check of pool qubes_dom0/vm-pool failed

I had a 4.3 upgrade Stage 3 failure where an old kernel-qubes-vm package couldn’t be removed. I fixed that issue and manually removed the package. I then manually ran the remaining commands (systemctl preset-all and systemctl enable) from the Stage 3 part of the upgrade script. I rebooted into Qubes 4.3 to complete Stages 4-6. After rebooting, none of my qubes are able to start. If I manually start a qube, I see this error: Error: Check of pool qubes_dom0/vm-pool failed (status:64). Manual rep…