How to access physical memory

Hi I'm the new here . And I have some questions with pmap.

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See `*pml4` is the physical address of a page with some flag. And then updated the address to the Direct Map Space. Then We calculate the offset of the real pdp we need .

How could it access to `*pdp`? it is a virtual addr in Direct Map Space. Why don't change the physical space directly since we have the physical page already.
 
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