> And what if the user program passes a pointer that is valid for the
> kernel to dereference (hence the MMU triggers no exception), but is not
> something userland code should be able to touch?
take a look at the access_ok() stuff in asm/uaccess.h. The kernel
explicitly checks the validity of the pointer in this sense. In contrast,
the former verify_area() call was a very expensive thing. (taking several
hundred cycles instead of 1-4 cycles, and being more expensive for bigger
memory maps)
-- mingo
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