Could you add a line to the description explicitly stating that a failure
to insert any page in the range will fail the entire routine, something
like:

* This allows drivers to insert range of kernel pages they've allocated
* into a user vma. This is a generic function which drivers can use
* rather than using their own way of mapping range of kernel pages into
* user vma.
*
* A failure to insert any page in the range will fail the call as a whole.

It's obvious when reading the code, but it would be self-documenting to
state it outright.

Thanks!
    -- Bill