I think they mean in regards to cross kernel attacks. vms didn't protect across speculative execution attacks.
I believe there are even more course grained timing attacks with dma and memory that are waiting to be abused.
tptacek
No, that's true, VMs don't protect against microarchitectural attacks. But neither does shared-kernel isolation; in fact, shared-kernel is even worse at it. So if that's the concern, it doesn't make much sense in the threat model.
burnt-resistor
Isolation guarantees: Separate metal > type 1 hypervisors > type 2 hypervisors > containers > processes > OS threads > cooperative threads ;)
I believe there are even more course grained timing attacks with dma and memory that are waiting to be abused.