Saxifraga paniculata minutifolia

Perhaps it is the small form. Variable, but much smaller leaves with lime encrustation. It forms a tight mat, excellent in troughs and crevices, add lime. Sun. ID fairly certain. In the image the rosettes are less than a centimetre across. Distinct form S. cochlearis minor as the leaves are less convoluted and more reflexed.  No guarantees for ID.