1/*
2 *   linux/mm/fremap.c
3 *
4 * Explicit pagetable population and nonlinear (random) mappings support.
5 *
6 * started by Ingo Molnar, Copyright (C) 2002, 2003
7 */
8
9#include <linux/mm.h>
10#include <linux/swap.h>
11#include <linux/file.h>
12#include <linux/mman.h>
13#include <linux/pagemap.h>
14#include <linux/swapops.h>
15#include <linux/rmap.h>
16#include <linux/module.h>
17#include <linux/syscalls.h>
18
19#include <asm/mmu_context.h>
20#include <asm/cacheflush.h>
21#include <asm/tlbflush.h>
22
23static int zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
24			unsigned long addr, pte_t *ptep)
25{
26	pte_t pte = *ptep;
27	struct page *page = NULL;
28
29	if (pte_present(pte)) {
30		flush_cache_page(vma, addr, pte_pfn(pte));
31		pte = ptep_clear_flush(vma, addr, ptep);
32		page = vm_normal_page(vma, addr, pte);
33		if (page) {
34			if (pte_dirty(pte))
35				set_page_dirty(page);
36			page_remove_rmap(page, vma);
37			page_cache_release(page);
38		}
39	} else {
40		if (!pte_file(pte))
41			free_swap_and_cache(pte_to_swp_entry(pte));
42		pte_clear_not_present_full(mm, addr, ptep, 0);
43	}
44	return !!page;
45}
46
47/*
48 * Install a file page to a given virtual memory address, release any
49 * previously existing mapping.
50 */
51int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
52		unsigned long addr, struct page *page, pgprot_t prot)
53{
54	struct inode *inode;
55	pgoff_t size;
56	int err = -ENOMEM;
57	pte_t *pte;
58	pte_t pte_val;
59	spinlock_t *ptl;
60
61	pte = get_locked_pte(mm, addr, &ptl);
62	if (!pte)
63		goto out;
64
65	/*
66	 * This page may have been truncated. Tell the
67	 * caller about it.
68	 */
69	err = -EINVAL;
70	inode = vma->vm_file->f_mapping->host;
71	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
72	if (!page->mapping || page->index >= size)
73		goto unlock;
74	err = -ENOMEM;
75	if (page_mapcount(page) > INT_MAX/2)
76		goto unlock;
77
78	if (pte_none(*pte) || !zap_pte(mm, vma, addr, pte))
79		inc_mm_counter(mm, file_rss);
80
81	flush_icache_page(vma, page);
82	pte_val = mk_pte(page, prot);
83	set_pte_at(mm, addr, pte, pte_val);
84	page_add_file_rmap(page);
85	update_mmu_cache(vma, addr, pte_val);
86	lazy_mmu_prot_update(pte_val);
87	err = 0;
88unlock:
89	pte_unmap_unlock(pte, ptl);
90out:
91	return err;
92}
93EXPORT_SYMBOL(install_page);
94
95/*
96 * Install a file pte to a given virtual memory address, release any
97 * previously existing mapping.
98 */
99int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
100		unsigned long addr, unsigned long pgoff, pgprot_t prot)
101{
102	int err = -ENOMEM;
103	pte_t *pte;
104	spinlock_t *ptl;
105
106	pte = get_locked_pte(mm, addr, &ptl);
107	if (!pte)
108		goto out;
109
110	if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte)) {
111		update_hiwater_rss(mm);
112		dec_mm_counter(mm, file_rss);
113	}
114
115	set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
116	/*
117	 * We don't need to run update_mmu_cache() here because the "file pte"
118	 * being installed by install_file_pte() is not a real pte - it's a
119	 * non-present entry (like a swap entry), noting what file offset should
120	 * be mapped there when there's a fault (in a non-linear vma where
121	 * that's not obvious).
122	 */
123	pte_unmap_unlock(pte, ptl);
124	err = 0;
125out:
126	return err;
127}
128
129/***
130 * sys_remap_file_pages - remap arbitrary pages of a shared backing store
131 *                        file within an existing vma.
132 * @start: start of the remapped virtual memory range
133 * @size: size of the remapped virtual memory range
134 * @prot: new protection bits of the range
135 * @pgoff: to be mapped page of the backing store file
136 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
137 *
138 * this syscall works purely via pagetables, so it's the most efficient
139 * way to map the same (large) file into a given virtual window. Unlike
140 * mmap()/mremap() it does not create any new vmas. The new mappings are
141 * also safe across swapout.
142 *
143 * NOTE: the 'prot' parameter right now is ignored, and the vma's default
144 * protection is used. Arbitrary protections might be implemented in the
145 * future.
146 */
147asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
148	unsigned long __prot, unsigned long pgoff, unsigned long flags)
149{
150	struct mm_struct *mm = current->mm;
151	struct address_space *mapping;
152	unsigned long end = start + size;
153	struct vm_area_struct *vma;
154	int err = -EINVAL;
155	int has_write_lock = 0;
156
157	if (__prot)
158		return err;
159	/*
160	 * Sanitize the syscall parameters:
161	 */
162	start = start & PAGE_MASK;
163	size = size & PAGE_MASK;
164
165	/* Does the address range wrap, or is the span zero-sized? */
166	if (start + size <= start)
167		return err;
168
169	/* Can we represent this offset inside this architecture's pte's? */
170#if PTE_FILE_MAX_BITS < BITS_PER_LONG
171	if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
172		return err;
173#endif
174
175	/* We need down_write() to change vma->vm_flags. */
176	down_read(&mm->mmap_sem);
177 retry:
178	vma = find_vma(mm, start);
179
180	/*
181	 * Make sure the vma is shared, that it supports prefaulting,
182	 * and that the remapped range is valid and fully within
183	 * the single existing vma.  vm_private_data is used as a
184	 * swapout cursor in a VM_NONLINEAR vma.
185	 */
186	if (vma && (vma->vm_flags & VM_SHARED) &&
187		(!vma->vm_private_data || (vma->vm_flags & VM_NONLINEAR)) &&
188		vma->vm_ops && vma->vm_ops->populate &&
189			end > start && start >= vma->vm_start &&
190				end <= vma->vm_end) {
191
192		/* Must set VM_NONLINEAR before any pages are populated. */
193		if (pgoff != linear_page_index(vma, start) &&
194		    !(vma->vm_flags & VM_NONLINEAR)) {
195			if (!has_write_lock) {
196				up_read(&mm->mmap_sem);
197				down_write(&mm->mmap_sem);
198				has_write_lock = 1;
199				goto retry;
200			}
201			mapping = vma->vm_file->f_mapping;
202			spin_lock(&mapping->i_mmap_lock);
203			flush_dcache_mmap_lock(mapping);
204			vma->vm_flags |= VM_NONLINEAR;
205			vma_prio_tree_remove(vma, &mapping->i_mmap);
206			vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
207			flush_dcache_mmap_unlock(mapping);
208			spin_unlock(&mapping->i_mmap_lock);
209		}
210
211		err = vma->vm_ops->populate(vma, start, size,
212					    vma->vm_page_prot,
213					    pgoff, flags & MAP_NONBLOCK);
214
215		/*
216		 * We can't clear VM_NONLINEAR because we'd have to do
217		 * it after ->populate completes, and that would prevent
218		 * downgrading the lock.  (Locks can't be upgraded).
219		 */
220	}
221	if (likely(!has_write_lock))
222		up_read(&mm->mmap_sem);
223	else
224		up_write(&mm->mmap_sem);
225
226	return err;
227}
228