Hi Sebastian, thanks for your reply! Actually I have only one VM running. This has KVM64 as CPU (default) configuration. PCID is not set. The VM hosts a UCS system which has already updated their part of Linux against Meltdown.Do you have also updated your VM kernels? or only your HOST kernel? If your VM have "host" cpu configuration, no need to pass this option, it only needed if you have other cpu type configurated.