Virtual machine – Meltdown attack cannot be used to break out of a virtual machine, i.e. in fully virtualized machines guest user space can still read from guest kernel space, but not from host kernel space.[35] The bug enables reading memory from address space represented by the same page table, meaning the bug does not work between virtual tables. That is, Guest-to-Host page tables are unaffected, only Guest-to-Guest or Host-to-Host, and of course Host-to-Guest since the host can already access the guest pages. This means
different VMs on the same fully virtualized hypervisor cannot access each others' data, but different users on the same guest instance can access each others' data.[36]
https://en.wikipedia.org/wiki/Meltdown_(security_vulnerability)