Does there exist a Kernel stack and a user-space stack for each user space process? If both stacks exist, there should be 2 stack pointers for each user space process right?
In Linux, each task (userspace or kernel thread) has a kernel stack of either 8kb or 4kb, depending on kernel configuration. There are indeed separate stack pointers, however, only one is present in the CPU at any given time; if userspace code is running, the kernel stack pointer to be used on exceptions or interrupts is specified by the task-state segment, and if kernel code is running, the user stack pointer is saved in the context structure located on the kernel stack.
来源：https://stackoverflow.com/questions/6083236/does-there-exist-kernel-stack-for-each-process