what is a "kernel (only) thread" as opposed to "kernel-level thread"? [duplicate]

This question already has answers here: 开发者_如何学编程 Closed 11 years ago.

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user thread and kernel thread

I recently came across the terms "kernel thread" / "kernel-only thread". It was defined as a thread which executes entirely in the kernel space and has no virtual address space. Can somebody please explain what it actually means and how is it implemented? This seems to quite different from kernel-level threads.Also, since the kernel itself is not a process how can there be a thread entirely in kernel space ?

I have seen the question on user thread and kernel thread but the answers are conflicting and the selected answer only gives a definition and not details.

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Taken from this

Kernel threads are used to provide privileged services to applications (such as system calls ). The are also used by the kernel to keep track of what all is running on the system, how much of which resources are allocated to what process, and to do scheduling.