The Machzor Vitry (§234) finds a scriptural source for Hanukkah in Leviticus 24:2. That the stipulation that Israelites should collect pure olive oil for the menorah should follow on from a description of the festivals would seem to suggest that there would one day be an additional festival that relates in some way to pure olive oil. This is the language of the Machzor Vitry:
רמז לחנוכה מן התורה שכת׳ אחר כל המועדות בפר׳ אמר ויקחו אליך שמן זית זך... ומדכתביה עם המועדות למדנו שהוא יום טוב כשאר ימים טובים
There is an allusion to Hanukkah in the Torah in that it is written, after all of the festivals in Parshat Emor, "collect pure olive oil for yourselves"... and since it is written together with the other festivals, it teaches us that it is a yom tov like the other yamim tovim.
The gemara also refers to the days of Hanukkah as yamim tovim (Shabbat 21b), but Rashi very carefully stipulates (s.v. ועשאום ימים טובים) that they are not yamim tovim in respect of any prohibition of work, but only in respect of one needing to recite hallel and al hannissim. This is important, since the usual definition of a yom tov is of a festival day on which work is forbidden (cf: Rambam, Hilkhot Shevitat Yom Tov 1:1).
That said, the festivals mentioned in Parshat Emor are all days on which it is forbidden to work, and the drash recorded in Machzor Vitry would seem to be explicitly likening Hanukkah to them. What is more, the stipulation that Hanukkah is a yom tov "like the other yamim tovim" would argue against its being a yom tov only in respect of the fact that one recites hallel and al hannissim on it, since one does not recite hallel on Rosh haShana, and one only recites al hannissim on Hanukkah and Purim.
My question is, in what sense can Hanukkah be said to be a yom tov "like the other yamim tovim", while still allowing for the permissibility of work? Also, and relatedly, in what sense can this passage be reconciled with the opinion of Rashi in Shabbat 21b? This question becomes more profound when you consider the fact that the author of the Machzor Vitry, R' Simchah ben Shmuel, was a student of Rashi, and that this opinion of his is brought as an addition to Rashi's commentary (מוסף רש״י) on Leviticus 24:2, in the Miqraot Gedolot.