only kernel can access copy_area ?

Hi, all 
     Thank you for these days' help.
     Now, I am learning about  ipc. And have a question again. Sorry for troubling you!
 
     About the copy_area,when A sends a message to B, only kernel A and user B can access 
the copy_area. But user A can not. Is these correct ? And why ?
     In my opinion, the page table of A's copy_area is copyed from B whick is user accessiable.
So,user A can access the copy_area. Is that right?
     Thank you
     ---Best regardsBo Liu
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