>> i've got two pointers.
>> 
>> one may or may not be a valid kernel pointer.  i can't tell.
>> 
>> the other may be a pointer into userspace or a pointer into kernel
>> space.  i can tell which kind it is, and if it's the latter, i'm
>> perfectly willing to assume that it's valid.
>
>I give up.  How can you tell if a pointer is to userspace or kernel
>space?

oh, because i have a third pointer (to a struct lwp) that will be null
(or not null) if the second pointer is into kernel space (or user
space).

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