Not a lot of context here: I take it this means mapping pages as writable or executable, but never both? And this is being applied to the kernel itself and the pages it maps into kernel space?
That's right. W^X is a policy that memory is either writable or executable, but not both. OpenBSD uses this model in userspace, now it's being taken a step further and applied to kernel space.
According to [1] it's W xor X. Interpreting that literally suggests that read only memory is disallowed as well. I'd be surprised if that's actually the case.
