Hello @Morzaram and @gsong! My understanding is that PCI: Fatal: No config space access function found is a harmless, while disconcerting, message coming from the Linux kernel on boot.
From the kernel mailing list, [PATCH] x86/hyperv: suppress "PCI: Fatal: No config space access function found" - Dexuan Cui :
A Generatin-2 Linux VM on Hyper-V doesn’t have the legacy PCI bus, and
users always see the scary warning, which is actually harmless. The patch
is made to suppress the warning.