linux - 什么是 "the kernel address space"？

Question

从 Understanding The Linux Kernel 开始，这里有一些关于内核线程与用户进程(即常规进程)的讨论:

Besides user processes, Unix systems include a few privileged processes called kernel threads with the following characteristics:

• They run in Kernel Mode in the kernel address space.

• They do not interact with users, and thus do not require terminal devices.

• They are usually created during system startup and remain alive until the system is shut down.

...

In Linux, kernel threads differ from regular processes in the following ways:

• Kernel threads run only in Kernel Mode, while regular processes run alternatively in Kernel Mode and in User Mode.

• Because kernel threads run only in Kernel Mode, they use only linear addresses greater than PAGE_OFFSET. Regular processes, on the other hand, use all four gigabytes of linear addresses, in either User Mode or Kernel Mode.

我听说过用户进程的虚拟地址空间，即常规进程，和 a portion of the address space is mapped to the kernel code and data .

我的问题:

• 我想知道上面引述中的“内核地址空间”是什么意思？
• 它不是用户进程的虚拟地址空间的一部分吗？
• 这是否意味着内核有自己的虚拟地址空间，就像用户进程有自己的虚拟地址空间一样？

Answer 1

本书使用术语“内核地址空间”来指代为内核分配的虚拟地址空间的分区。

最近，Linux 和其他操作系统已经实现了 page-table isolation (PTI) 来缓解 Meltdown 安全漏洞。使用 PTI，内核确实有自己的地址空间(如维基百科的图片所示)。但由于这本书很旧，它是在 PTI 还没有发明的时候写的。

所以肯定是指虚拟地址空间的内核分区，其中也包含用户分区。