whatsnew (#31665)

(cherry picked from commit 103840e)

Author: TomAugspurger

doc/source/whatsnew/v1.0.1.rst

@@ -27,6 +27,7 @@ Fixed regressions
 - Fixed regression in objTOJSON.c fix return-type warning (:issue:`31463`)
 - Fixed regression in :meth:`qcut` when passed a nullable integer. (:issue:`31389`)
 - Fixed regression in assigning to a :class:`Series` using a nullable integer dtype (:issue:`31446`)
+- Fixed performance regression when indexing a ``DataFrame`` or ``Series`` with a :class:`MultiIndex` for the index using a list of labels (:issue:`31648`)
 
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