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}