Pain in gums where crown is placed? is that cavity or gingivitis?

It is possible: A little more history about the onset and type of pain you are experiencing is necessary. If the crown has been in place for a long period of time, you could have recurrent decay in the tooth. You could also have a periodontal or gum problem. If the crown is a new crown, it could be related to irritation from the seating of the crown, possibly some residual cement , or your occlusion or bite.

Gum pain: Gum pain - is the gums not tooth. Tooth pain would be cavity. So it is due most likely to trauma to the gum from the crown. See a periodontist.

Maybe: It could be several different things. You should definitely see your dentist or dental hygienist. You may be packing food in between the crown and your natural tooth. This is easy to resolve. You may have gingivitis to address through dental hygiene. Further, an x-ray can help your dentist see if you decay beneath the crown, or perhaps an adjacent tooth. See your dentist soon!