double fault -> PAGE_KERNEL flagged memory

[Roland McGrath]

> Then this is analogous to the problem of calling printk from within an
> inconveniently placed kprobe.  What can we do to eliminate this
> vulnerability?  Can we somehow arrange to "fault in" all probe-related
> kernel-space vmalloc areas into new process' address spaces, so we don't
> encounter this unintentional and undesirable reentrancy?

What's the reason for using vmalloc then?  Why not use kmalloc that doesn't
need page table changes?