See also the FAQ entry.
IRC, freenode, #hurd, 2012-09-30
<braunr> i expect smp to be our next gsoc project
IRC, freenode, #hurd, 2013-01-02
<braunr> i'd like to mentor someone for adding smp to gnumach
IRC, freenode, #hurd, 2013-03-14
<braunr> but i'm afraid we'll have to fight obscur smp-safety issues <braunr> for one, drivers are much probably not smp safe and would require a big kernel lock <braunr> userspace (such as signal delivery in libc) might be affected too <braunr> smp isn't that easy
This task actually looks too big for a GSoC project.