Understanding the Linux Kernel, 3rd Edition

Page Fault Exception Handler

As stated previously, the Linux Page Fault exception handler must distinguish exceptions caused by programming errors from those caused by a reference to a page that legitimately belongs to the process address space but simply hasn’t been allocated yet.

The memory region descriptors allow the exception handler to perform its job quite efficiently. The do_page_fault( ) function, which is the Page Fault interrupt service routine for the 80 × 86 architecture, compares the linear address that caused the Page Fault against the memory regions of the current process; it can thus determine the proper way to handle the exception according to the scheme that is illustrated in Figure 9-4.

Figure 9-4. Overall scheme for the Page Fault handler

In practice, things are a lot more complex because the Page Fault handler must recognize several particular subcases that fit awkwardly into the overall scheme, and it must distinguish several kinds of legal access. A detailed flow diagram of the handler is illustrated in Figure 9-5.

The identifiers vmalloc_fault, good_area, bad_area, and no_context are labels appearing in do_page_fault( ) that should help you to relate the blocks of the flow diagram to specific lines of code.

The do_ page_fault( ) function accepts the following input parameters:

• The regs address of a pt_regs structure containing the values of the microprocessor ...