1/*
2 *  flexible mmap layout support
3 *
4 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
5 * All Rights Reserved.
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
20 *
21 *
22 * Started by Ingo Molnar <mingo@elte.hu>
23 */
24
25#include <linux/personality.h>
26#include <linux/mm.h>
27#include <linux/sched.h>
28
29/*
30 * Top of mmap area (just below the process stack).
31 *
32 * Leave an at least ~128 MB hole.
33 */
34#define MIN_GAP (128*1024*1024)
35#define MAX_GAP (TASK_SIZE/6*5)
36
37static inline unsigned long mmap_base(void)
38{
39	unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
40
41	if (gap < MIN_GAP)
42		gap = MIN_GAP;
43	else if (gap > MAX_GAP)
44		gap = MAX_GAP;
45
46	return TASK_SIZE - (gap & PAGE_MASK);
47}
48
49static inline int mmap_is_legacy(void)
50{
51	/*
52	 * Force standard allocation for 64 bit programs.
53	 */
54	if (!test_thread_flag(TIF_32BIT))
55		return 1;
56
57	if (current->personality & ADDR_COMPAT_LAYOUT)
58		return 1;
59
60	if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
61		return 1;
62
63	return sysctl_legacy_va_layout;
64}
65
66/*
67 * This function, called very early during the creation of a new
68 * process VM image, sets up which VM layout function to use:
69 */
70void arch_pick_mmap_layout(struct mm_struct *mm)
71{
72	/*
73	 * Fall back to the standard layout if the personality
74	 * bit is set, or if the expected stack growth is unlimited:
75	 */
76	if (mmap_is_legacy()) {
77		mm->mmap_base = TASK_UNMAPPED_BASE;
78		mm->get_unmapped_area = arch_get_unmapped_area;
79		mm->unmap_area = arch_unmap_area;
80	} else {
81		mm->mmap_base = mmap_base();
82		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
83		mm->unmap_area = arch_unmap_area_topdown;
84	}
85}
86