LXR linux/lib/devmem_is

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * A generic version of devmem_is_allowed.
   4 *
   5 * Based on arch/arm64/mm/mmap.c
   6 *
   7 * Copyright (C) 2020 Google, Inc.
   8 * Copyright (C) 2012 ARM Ltd.
   9 */
  10
  11#include <linux/mm.h>
  12#include <linux/ioport.h>
  13
  14/*
  15 * devmem_is_allowed() checks to see if /dev/mem access to a certain address
  16 * is valid. The argument is a physical page number.  We mimic x86 here by
  17 * disallowing access to system RAM as well as device-exclusive MMIO regions.
  18 * This effectively disable read()/write() on /dev/mem.
  19 */
  20int devmem_is_allowed(unsigned long pfn)
  21{
  22        if (iomem_is_exclusive(PFN_PHYS(pfn)))
  23                return 0;
  24        if (!page_is_ram(pfn))
  25                return 1;
  26        return 0;
  27}
  28