  Motivated by open problems in F-theory, we reconsider warped
compactifications of M theory on 8-manifolds to AdS3 spaces in the presence of
a non-trivial field strength of the M-theory 3-form, studying the most general
conditions under which such backgrounds preserve N=2 supersymmetry in three
dimensions. In contrast with previous studies, we allow for the most general
pair of Majorana generalized Killing pinors on the internal 8-manifold, without
imposing any chirality conditions on those pinors. We also show how such pinors
can be lifted to the 9-dimensional metric cone over the compactification
8-manifold. We describe the translation of the generalized Killing pinor
equations for such backgrounds to a system of differential and algebraic
constraints on certain form-valued pinor bilinears and develop techniques
through which such equations can be analyzed efficiently.
