Host measures should stop the attacks between VMs, but they will not stop attacks within a VM. A busy VM threads may run on their physical cores/threads uninter

Host measures should stop the attacks between VMs, but they will not stop attacks within a VM. A busy VM threads may run on their physical cores/threads uninterrupted by the host. Flashing branch prediction by the host on a context switch then does not happen so this variant of Spectre still works. The host measures will not protect against another variant of Spectre or Meltdown within the VM even if the host performs context switches. The frequency of switches is just too low to disrupt a single cycle of the attack. So the attack will be just slowed down. In addition, as processes within VM have both access to high-resolution timer and CPU performance counters, the attack can detect context switches allowing for simpler recovery from them.