As far as I know, yes. It's a variation of the common expression: "It's all ok", here "perfectly" adds extra reassurance. The grammatical construction used here can be recognised as such: PRONOUN + it's (to be) + all + COMPLEMENT. "All" is used to qualify the pronoun, giving a sense of entirety. Other examples: They are all aliens. It's all green. (Eg. talking about a house) We are all humans. Take a look at section 3.1 here: http://linguapress.com/grammar/points/all-whole.htm. A

Sure thing it is!