Why do systems generally disable virtualization by default in BIOS settings

virtualization

I have yet to see a system whose default configuration enables MMU and directed I/O virtualization. Often this necessitates rebooting and going into the BIOS to enable it if you want, e.g., 64-bit support on your VMs.

Is there some kind of substantial processor overhead that occurs if this is switched on and you're not using virtualization? If not, then what's the reason for it being off by default?

Best Answer

There were some proof-of-concept rootkits like Blue Pill a while back that could own a system with VT on. After this discovery, most vendors began shipping their units with VT disabled as a general security precaution.

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