QEMU hangs with smp option on ubuntu 16.04 ... any fix?

Hi, all,

I've been loosely following the instruct at this page,
https://github.com/kholia/mips-hacking

My host is ubuntu 16.04.  I used ubuntu prebuilt qemu system images.

My guest is the latest stretch 9.5 malta netboot images.  Kernel is
vmlinux-4.9.0-7-4kc-malta.

Below is my startup script.  If I change "smp" to 2, the startup will hang
very early on.   Does anybody if this is a known limit with debian distro?
Or it is an issue with the ubuntu prebuilt qemu?  Or there are some other
gotcha's here?

qemu-system-mips \
-M malta \
-m 256 \
-hda hda.qcow2 \
-kernel vmlinux-4.9.0-7-4kc-malta \
-initrd initrd.img-4.9.0-7-4kc-malta \
    -append "root=/dev/sda1 console=ttyS0 nokaslr" \
-nographic \
-redir tcp:2222::22 \
-smp 1 \
\

Cheers.

Jun