vmf_insert_pfn is added with the following commit. https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1c8f422059ae5da07db7406ab916203f9417e396 Refer to the following page for the meaning of VM_FAULT_NOPAGE. https://lwn.net/Articles/242237/ Change-Id: I2b0144a20a57c74e0e2e0d2fc24281852f49b717