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Multi-core systems are the potential enablers of the overwhelming growth of mixed criticality systems. There exist challenges to the widespread usage of multi-core in mixed criticality systems due to the non-predictive resource access timings. In this work, we present an LLC access control mechanism, MEDIATOR that guarantees high criticality job executions without deadline misses for multi-core mixed-criticality systems. In MEDIATOR, the LLC access requests of lower criticality jobs are honored, if and only if there exists adequate slack for higher criticality jobs. The legacy FIFO arbiter has a greater probability of deadline misses for high criticality jobs. The MEDIATOR behaves like legacy FIFO when there is sufficient slack. When the slack of the higher criticality jobs is less, it blocks low criticality jobs for the successful execution of higher criticality jobs. The experimental evaluation with software simulation and hardware implementation confirms the successful completion of high criticality jobs with LLC contention by honoring low criticality jobs whenever possible. Simulation results with the help of synthetic benchmark shows successful completion of high criticality jobs at a high workload where legacy FIFO fails. The hardware design synthesized in Cadence using Genus Synthesis Solution 17.21−s010_1 shows that MEDIATOR takes negligibly small time overhead and energy consumption to achieve the same.