text: /*
   * Based on arch/arm/mm/mmap.c
   *
   * Copyright (C) 2012 ARM Ltd.
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
   */
  
  #include <linux/elf.h>
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/mman.h>
  #include <linux/export.h>
  #include <linux/shm.h>
  #include <linux/sched.h>
  #include <linux/io.h>
  #include <linux/personality.h>
  #include <linux/random.h>
  
  #include <asm/cputype.h>
  
  /*
   * Leave enough space between the mmap area and the stack to honour ulimit in
   * the face of randomisation.
   */
  #define MIN_GAP (SZ_128M + ((STACK_RND_MASK << PAGE_SHIFT) + 1))
  #define MAX_GAP	(STACK_TOP/6*5)
  
  static int mmap_is_legacy(void)
  {
  	if (current->personality & ADDR_COMPAT_LAYOUT)
  		return 1;
  
  	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  		return 1;
  
  	return sysctl_legacy_va_layout;
  }
  
  static unsigned long mmap_rnd(void)
  {
  	unsigned long rnd = 0;
  
  	 if (current->flags & PF_RANDOMIZE) {
  #ifdef CONFIG_COMPAT
  		if (test_thread_flag(TIF_32BIT))
  			rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
  		else
  #endif
  			rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
  	}
  	return rnd << PAGE_SHIFT;
  }
  
  static unsigned long mmap_base(void)
  {
  	unsigned long gap = rlimit(RLIMIT_STACK);
  
  	if (gap < MIN_GAP)
  		gap = MIN_GAP;
  	else if (gap > MAX_GAP)
  		gap = MAX_GAP;
  
  	return PAGE_ALIGN(STACK_TOP - gap - mmap_rnd());
  }
  
  /*
   * This function, called very early during the creation of a new process VM
   * image, sets up which VM layout function to use:
   */
  void arch_pick_mmap_layout(struct mm_struct *mm)
  {
  	/*
  	 * Fall back to the standard layout if the personality bit is set, or
  	 * if the expected stack growth is unlimited:
  	 */
  	if (mmap_is_legacy()) {
  		mm->mmap_base = TASK_UNMAPPED_BASE;
  		mm->get_unmapped_area = arch_get_unmapped_area;
  	} else {
  		mm->mmap_base = mmap_base();
  		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  	}
  }
  EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
  
  
  /*
   * You really shouldn't be using read() or write() on /dev/mem.  This might go
   * away in the future.
   */
  int valid_phys_addr_range(unsigned long addr, size_t size)
  {
  	if (addr < PHYS_OFFSET)
  		return 0;
  	if (addr + size > __pa(high_memory - 1) + 1)
  		return 0;
  
  	return 1;
  }
  
  /*
   * Do not allow /dev/mem mappings beyond the supported physical range.
   */
  int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
  {
  	return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
  }
  
  #ifdef CONFIG_STRICT_DEVMEM
  
  #include <linux/ioport.h>
  
  /*
   * devmem_is_allowed() checks to see if /dev/mem access to a certain address
   * is valid. The argument is a physical page number.  We mimic x86 here by
   * disallowing access to system RAM as well as device-exclusive MMIO regions.
   * This effectively disable read()/write() on /dev/mem.
   */
  int devmem_is_allowed(unsigned long pfn)
  {
  	if (iomem_is_exclusive(pfn << PAGE_SHIFT))
  		return 0;
  	if (!page_is_ram(pfn))
  		return 1;
  	return 0;
  }
  
  #endif
  