Spintronics-based non-volatile storage devices promise great potential to be integrated in reconfigurable circuits to overcome the major hurdles related to conventional flash and SRAM memories, such as low logic density, high standby power and long (re) boot latency. In this paper, we describe a compact design of configurable logic block based on Magnetic RAM (MRAM) crossbar architecture. The logic density can be increased greatly (~5 times) compared to conventional designs; the standby power can be nearly zero thanks to the non-volatility of MRAM. Its high speed and power efficiency (~10.4 Tera-OPS/Watt in computing mode) are also demonstrated through mixed CMOS/Magnetic spice simulations. Fully dynamic reconfiguration through context switching is also studied, which could be achieved with low area overhead.