exe.dev explains crossing the hyper-thread boundary: core scheduling cookies for VM isolation
davidcrawshaw · x · 2026-10-08
exe.dev, which rents per-second VMs for AI agents, published a blog on the security cost of hyper-threading and their isolation approach:
- Two logical cores on one physical core share resources, exposing transient-execution attacks (e.g. MDS) that can leak data across hyper-threads
- Giving each VM its own core scheduling cookie is simple but measurably wastes physical cores
- Their compromise: VMs within a team share a cookie (assuming intra-team trust), while VMs from different teams never share a core
- Team admins can disable internal sharing via ssh exe.dev team settings core-sharing off
- The authors believe their exposure of kernel scheduling cookie control is novel
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