Rebecca Hall came across Nella Larsen’s novel “Passing” at a time when she was grappling with her own family history. She’d become aware that her maternal grandfather was “white passing,” and it might have gone back even further. Then someone handed her this book, from 1929, about two childhood friends who meet again as adults. Both Clare and Irene are light-skinned Black women and Clare has been living as white. And it was the beginning of a lengthy journey to making her first film, “Passing,” starring Ruth Negga and Tessa Thompson, which premiered this weekend at the Sundance Film Festival to wide acclaim.