How to artificially cause a page fault in linux kernel?

When accessing a given address, how does the Linux kernel know that a particular page is mmaped?

• I want to know, given an address X, how does the Linux kernel figure out that X is an mmaped page? Is there a special flag in the page table entry? Does the access generate a page fault ? If so, how does the handler find out it is an mmaped address?

• Answer:

  When you first access an mmaped page, the page fault handler runs. On most architectures, this invokes an architecture-specific function named do_page_fault(). This function checks some basics: Is this kernel memory? If not, are we in an interrupt handler? If not, the kernel attempts to find the memory range within one of the vm_area_struct structures associated with this process's address space. The vm_area_struct structure describes regions of the process address space that share page fault behavior—for example, paging in an mmaped file. The kernel calls these regions virtual memory areas or VMAs. If a VMA containing the faulted address exists and is valid for the type of access performed, the kernel then invokes handle_mm_fault() to perform whatever action is needed to page in the contents of the requested page. The vm_area_struct will describe the mmaped file and allow handle_mm_fault() to page in the requisite data. The short summary: Yes, a page fault occurs and the page fault handler is executed. The fact that the memory address corresponds to an mmaped page is noted by the vm_area_struct structure for that particular address.