Update the comment at the head of kmem_alloc_nofault() to describe its

purpose and use.

sys/vm/vm_kern.c

@@ -119,7 +119,11 @@ kmem_alloc_pageable(map, size)
 /*
  *	kmem_alloc_nofault:
  *
- *	Same as kmem_alloc_pageable, except that it create a nofault entry.
+ *	Allocate a virtual address range with no underlying object and
+ *	no initial mapping to physical memory.  Any mapping from this
+ *	range to physical memory must be explicitly created prior to
+ *	its use, typically with pmap_qenter().  Any attempt to create
+ *	a mapping on demand through vm_fault() will result in a panic. 
  */
 vm_offset_t
 kmem_alloc_nofault(map, size)