# How to access physical memory



## scw00 (Dec 23, 2018)

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






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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## acheron (Dec 23, 2018)

Such question should be asked on freebsd-current@ or freebsd-hackers@


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## scw00 (Dec 24, 2018)

Thanks， Will send an email soon.


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