Phoronix published An Early Look At The L1 Terminal Fault "L1TF" Performance Impact On Virtual Machines (Foreshadow) A quote from the article:

Yesterday the latest speculative execution vulnerability was disclosed that was akin to Meltdown and is dubbed the L1 Terminal Fault, or "L1TF" for short. Here are some very early benchmarks of the performance impact of the L1TF mitigation on the Linux virtual machine performance when testing the various levels of mitigation as well as the unpatched system performance prior to this vulnerability coming to light.

 An Early Look At The L1 Terminal Fault "L1TF" Performance Impact On Virtual Machines (Foreshadow)