Top and bottom of this picture appear to be the HBM2 interfaces. Despite the width of GP100’s 4096-bit HBM2 bus, the space consumed by HBM2 appears to be relatively small on the admittedly large GPU, which is one of the benefits of HBM as it allows for very tight routing and simpler GPU-side logic. Going HBM didn’t just get NVIDIA more memory bandwidth, but I fully expect it also got them a meaningful increase in die area that they could dedicate to GPU logic.
There is also a new high-quality hot of the GP100 package, this shows of the tight spacing between the GPU and the HBM2 stacks.
More details at AnandTech.