You have a Hyper-V host. You are evaluating the available schedulers. Which type of scheduler maximizes isolation between guests and the host?

Question

Options

• Aclassic
• Broot
• Ccore
• Dclassic with Simultaneous Multithreading (SMT) disabled

• A
  5% (1)
• C
  95% (20)

Explanation

The Hyper-V core scheduler maximizes isolation between guests and the host by enforcing that virtual processors (VPs) belonging to the same VM always run on SMT siblings (hyperthreads) of the same physical core - and crucially, VPs from different VMs (or the host) are never co-scheduled on the same physical core's SMT siblings simultaneously. This eliminates the microarchitectural sharing that enables side-channel attacks like L1TF and Spectre variant 2, where a malicious guest could leak information from the host or another VM via shared CPU execution resources. The classic scheduler (A) ignores SMT topology entirely, allowing VPs from different VMs or the host to share a physical core - maximizing utilization but sacrificing isolation. Classic with SMT disabled (D) achieves similar isolation to the core scheduler by turning off hyperthreading completely, but it wastes half the logical CPU capacity and is a blunter instrument. The root scheduler (B) gives the root partition (Windows host OS) full control over scheduling decisions but does not inherently enforce cross-VM isolation.

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