Since kvm-73 you will notice that when starting kvm, the message "vmport: uknown command 13" pops up on the terminal and probably wondering what this message means. It turns out that this message is totally harmless. Chris Lalancette went on to describe this on the mailing list as follows:

It's actually harmless; it's the Bochs BIOS trying to access the vmport function 13, which means "give me your UUID". However, upstream Qemu (and hence, KVM) doesn't support this function, so that's where the error message comes from. If I understand it correctly, upstream Qemu now has suppressed this warning message, so the next time KVM syncs up, the message will disappear.

Chris Marcelo Arenas Belon describes the bug on the mailing list as follows.

it is a bug from qemu's vmware backdoor that has been fixed already upstream, and that shouldn't be printed unless debugging that interface (not all commands had been implemented already)

it is harmless and can be ignored for now or you can just pull the patch from qemu upstream if you don't want to wait until the next merge :

The patch can be found at the link below

patch to remove vmport uknown command 13 bug