Advisor recommended reuse excerpt of master's dissertation in Ph.D. Thesis
I would treat a long excerpt of your own material acceptable provided that you also cite it, listing carefully that it is an excerpt and pointing to the original source. I'm assuming that you hold copyright on the early work, not having yielded it to another publisher. 

Don't confuse the two issues, permission to create a derived work, and proper citation. The permission is obvious if you hold copyright and by citation you avoid any claim of self plagiarism. 

Note that the main purpose of avoiding self plagiarism is to let readers find the original source of material and, thus, learn its complete context. By citing, you make this possible.