The KPTI patches to mitigate Meltdown can incur massive overhead, anything from 1% to over 800%. Where you are on that spectrum depends on your syscall and page fault rates, due to the extra CPU cycle overheads, and your memory working set size, due to TLB flushing on syscalls and context switches.
My Virtual Machines aged 5 years overnight; the performance hit has been more than the highest estimates of 30%. But I never thought the fallout could introduce penalties as high as 800%. Crazy.