Phoronix published The Performance Impact Of MDS / Zombieload Plus The Overall Cost Now Of Spectre/Meltdown/L1TF/MDS A quote from the article:

The past few days I've begun exploring the performance implications of the new Microarchitectural Data Sampling "MDS" vulnerabilities now known more commonly as Zombieload. As I shared in some initial results, there is a real performance hit to these mitigations. In this article are more MDS/Zombieload mitigation benchmarks on multiple systems as well as comparing the overall performance impact of the Meltdown/Spectre/Foreshadow/Zombieload mitigations on various Intel CPUs and also AMD CPUs where relevant.

 The Performance Impact Of MDS / Zombieload Plus The Overall Cost Now Of Spectre/Meltdown/L1TF/MDS