[yjftsjthsd-h]

I believe (IANAL) the implementation of KVM is GPL because it's part of Linux, but that's not viral into user space.

[CommanderData]

I'm no expert on licensing but I seem to remember GPL requires making available source if using and if the GPL project is modified, though I could be entirely mistaken.

[epcoa]

They’re making modifications to kernel code, which they’re upstreaming. They don’t need to open anything that’s on the user side of the syscall interface.

There’s plenty of closed source software that runs on Linux, VMware workstation included.