I'm spinning up a guest, using virt-install.  i'm passing the guest a single vcpu and many network interfaces.  On the guest side all the interfaces are initially in the down state.  I've notice then when I manually bring a specific one of these interfaces up (eg the 64th interface), the guest system hangs.  Doing an "strace ifconfig etX up", it looks like the system hangs when doing the ioctl to bring the interface up.

This guest is 18.04.  Host is 16.04.

Are there any qemu/virt commands i can run from the host which would provide me a better understanding as to why the guest gets into this hung state?

If I pass two vcpu, I don't suffer from this hang issue.