filemap_xip.c revision 54cb8821de07f2ffcd28c380ce9b93d5784b40d7 
1/*
2 *	linux/mm/filemap_xip.c
3 *
4 * Copyright (C) 2005 IBM Corporation
5 * Author: Carsten Otte <cotte@de.ibm.com>
6 *
7 * derived from linux/mm/filemap.c - Copyright (C) Linus Torvalds
8 *
9 */
10
11#include <linux/fs.h>
12#include <linux/pagemap.h>
13#include <linux/module.h>
14#include <linux/uio.h>
15#include <linux/rmap.h>
16#include <linux/sched.h>
17#include <asm/tlbflush.h>
18#include "filemap.h"
19
20/*
21 * We do use our own empty page to avoid interference with other users
22 * of ZERO_PAGE(), such as /dev/zero
23 */
24static struct page *__xip_sparse_page;
25
26static struct page *xip_sparse_page(void)
27{
28	if (!__xip_sparse_page) {
29		unsigned long zeroes = get_zeroed_page(GFP_HIGHUSER);
30		if (zeroes) {
31			static DEFINE_SPINLOCK(xip_alloc_lock);
32			spin_lock(&xip_alloc_lock);
33			if (!__xip_sparse_page)
34				__xip_sparse_page = virt_to_page(zeroes);
35			else
36				free_page(zeroes);
37			spin_unlock(&xip_alloc_lock);
38		}
39	}
40	return __xip_sparse_page;
41}
42
43/*
44 * This is a file read routine for execute in place files, and uses
45 * the mapping->a_ops->get_xip_page() function for the actual low-level
46 * stuff.
47 *
48 * Note the struct file* is not used at all.  It may be NULL.
49 */
50static void
51do_xip_mapping_read(struct address_space *mapping,
52		    struct file_ra_state *_ra,
53		    struct file *filp,
54		    loff_t *ppos,
55		    read_descriptor_t *desc,
56		    read_actor_t actor)
57{
58	struct inode *inode = mapping->host;
59	unsigned long index, end_index, offset;
60	loff_t isize;
61
62	BUG_ON(!mapping->a_ops->get_xip_page);
63
64	index = *ppos >> PAGE_CACHE_SHIFT;
65	offset = *ppos & ~PAGE_CACHE_MASK;
66
67	isize = i_size_read(inode);
68	if (!isize)
69		goto out;
70
71	end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
72	for (;;) {
73		struct page *page;
74		unsigned long nr, ret;
75
76		/* nr is the maximum number of bytes to copy from this page */
77		nr = PAGE_CACHE_SIZE;
78		if (index >= end_index) {
79			if (index > end_index)
80				goto out;
81			nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
82			if (nr <= offset) {
83				goto out;
84			}
85		}
86		nr = nr - offset;
87
88		page = mapping->a_ops->get_xip_page(mapping,
89			index*(PAGE_SIZE/512), 0);
90		if (!page)
91			goto no_xip_page;
92		if (unlikely(IS_ERR(page))) {
93			if (PTR_ERR(page) == -ENODATA) {
94				/* sparse */
95				page = ZERO_PAGE(0);
96			} else {
97				desc->error = PTR_ERR(page);
98				goto out;
99			}
100		}
101
102		/* If users can be writing to this page using arbitrary
103		 * virtual addresses, take care about potential aliasing
104		 * before reading the page on the kernel side.
105		 */
106		if (mapping_writably_mapped(mapping))
107			flush_dcache_page(page);
108
109		/*
110		 * Ok, we have the page, so now we can copy it to user space...
111		 *
112		 * The actor routine returns how many bytes were actually used..
113		 * NOTE! This may not be the same as how much of a user buffer
114		 * we filled up (we may be padding etc), so we can only update
115		 * "pos" here (the actor routine has to update the user buffer
116		 * pointers and the remaining count).
117		 */
118		ret = actor(desc, page, offset, nr);
119		offset += ret;
120		index += offset >> PAGE_CACHE_SHIFT;
121		offset &= ~PAGE_CACHE_MASK;
122
123		if (ret == nr && desc->count)
124			continue;
125		goto out;
126
127no_xip_page:
128		/* Did not get the page. Report it */
129		desc->error = -EIO;
130		goto out;
131	}
132
133out:
134	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
135	if (filp)
136		file_accessed(filp);
137}
138
139ssize_t
140xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
141{
142	read_descriptor_t desc;
143
144	if (!access_ok(VERIFY_WRITE, buf, len))
145		return -EFAULT;
146
147	desc.written = 0;
148	desc.arg.buf = buf;
149	desc.count = len;
150	desc.error = 0;
151
152	do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
153			    ppos, &desc, file_read_actor);
154
155	if (desc.written)
156		return desc.written;
157	else
158		return desc.error;
159}
160EXPORT_SYMBOL_GPL(xip_file_read);
161
162/*
163 * __xip_unmap is invoked from xip_unmap and
164 * xip_write
165 *
166 * This function walks all vmas of the address_space and unmaps the
167 * __xip_sparse_page when found at pgoff.
168 */
169static void
170__xip_unmap (struct address_space * mapping,
171		     unsigned long pgoff)
172{
173	struct vm_area_struct *vma;
174	struct mm_struct *mm;
175	struct prio_tree_iter iter;
176	unsigned long address;
177	pte_t *pte;
178	pte_t pteval;
179	spinlock_t *ptl;
180	struct page *page;
181
182	page = __xip_sparse_page;
183	if (!page)
184		return;
185
186	spin_lock(&mapping->i_mmap_lock);
187	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
188		mm = vma->vm_mm;
189		address = vma->vm_start +
190			((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
191		BUG_ON(address < vma->vm_start || address >= vma->vm_end);
192		pte = page_check_address(page, mm, address, &ptl);
193		if (pte) {
194			/* Nuke the page table entry. */
195			flush_cache_page(vma, address, pte_pfn(*pte));
196			pteval = ptep_clear_flush(vma, address, pte);
197			page_remove_rmap(page, vma);
198			dec_mm_counter(mm, file_rss);
199			BUG_ON(pte_dirty(pteval));
200			pte_unmap_unlock(pte, ptl);
201			page_cache_release(page);
202		}
203	}
204	spin_unlock(&mapping->i_mmap_lock);
205}
206
207/*
208 * xip_fault() is invoked via the vma operations vector for a
209 * mapped memory region to read in file data during a page fault.
210 *
211 * This function is derived from filemap_fault, but used for execute in place
212 */
213static struct page *xip_file_fault(struct vm_area_struct *area,
214					struct fault_data *fdata)
215{
216	struct file *file = area->vm_file;
217	struct address_space *mapping = file->f_mapping;
218	struct inode *inode = mapping->host;
219	struct page *page;
220	pgoff_t size;
221
222	/* XXX: are VM_FAULT_ codes OK? */
223
224	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
225	if (fdata->pgoff >= size) {
226		fdata->type = VM_FAULT_SIGBUS;
227		return NULL;
228	}
229
230	page = mapping->a_ops->get_xip_page(mapping,
231					fdata->pgoff*(PAGE_SIZE/512), 0);
232	if (!IS_ERR(page))
233		goto out;
234	if (PTR_ERR(page) != -ENODATA) {
235		fdata->type = VM_FAULT_OOM;
236		return NULL;
237	}
238
239	/* sparse block */
240	if ((area->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
241	    (area->vm_flags & (VM_SHARED| VM_MAYSHARE)) &&
242	    (!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
243		/* maybe shared writable, allocate new block */
244		page = mapping->a_ops->get_xip_page(mapping,
245					fdata->pgoff*(PAGE_SIZE/512), 1);
246		if (IS_ERR(page)) {
247			fdata->type = VM_FAULT_SIGBUS;
248			return NULL;
249		}
250		/* unmap page at pgoff from all other vmas */
251		__xip_unmap(mapping, fdata->pgoff);
252	} else {
253		/* not shared and writable, use xip_sparse_page() */
254		page = xip_sparse_page();
255		if (!page) {
256			fdata->type = VM_FAULT_OOM;
257			return NULL;
258		}
259	}
260
261out:
262	fdata->type = VM_FAULT_MINOR;
263	page_cache_get(page);
264	return page;
265}
266
267static struct vm_operations_struct xip_file_vm_ops = {
268	.fault	= xip_file_fault,
269};
270
271int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
272{
273	BUG_ON(!file->f_mapping->a_ops->get_xip_page);
274
275	file_accessed(file);
276	vma->vm_ops = &xip_file_vm_ops;
277	vma->vm_flags |= VM_CAN_NONLINEAR;
278	return 0;
279}
280EXPORT_SYMBOL_GPL(xip_file_mmap);
281
282static ssize_t
283__xip_file_write(struct file *filp, const char __user *buf,
284		  size_t count, loff_t pos, loff_t *ppos)
285{
286	struct address_space * mapping = filp->f_mapping;
287	const struct address_space_operations *a_ops = mapping->a_ops;
288	struct inode 	*inode = mapping->host;
289	long		status = 0;
290	struct page	*page;
291	size_t		bytes;
292	ssize_t		written = 0;
293
294	BUG_ON(!mapping->a_ops->get_xip_page);
295
296	do {
297		unsigned long index;
298		unsigned long offset;
299		size_t copied;
300
301		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
302		index = pos >> PAGE_CACHE_SHIFT;
303		bytes = PAGE_CACHE_SIZE - offset;
304		if (bytes > count)
305			bytes = count;
306
307		/*
308		 * Bring in the user page that we will copy from _first_.
309		 * Otherwise there's a nasty deadlock on copying from the
310		 * same page as we're writing to, without it being marked
311		 * up-to-date.
312		 */
313		fault_in_pages_readable(buf, bytes);
314
315		page = a_ops->get_xip_page(mapping,
316					   index*(PAGE_SIZE/512), 0);
317		if (IS_ERR(page) && (PTR_ERR(page) == -ENODATA)) {
318			/* we allocate a new page unmap it */
319			page = a_ops->get_xip_page(mapping,
320						   index*(PAGE_SIZE/512), 1);
321			if (!IS_ERR(page))
322				/* unmap page at pgoff from all other vmas */
323				__xip_unmap(mapping, index);
324		}
325
326		if (IS_ERR(page)) {
327			status = PTR_ERR(page);
328			break;
329		}
330
331		copied = filemap_copy_from_user(page, offset, buf, bytes);
332		flush_dcache_page(page);
333		if (likely(copied > 0)) {
334			status = copied;
335
336			if (status >= 0) {
337				written += status;
338				count -= status;
339				pos += status;
340				buf += status;
341			}
342		}
343		if (unlikely(copied != bytes))
344			if (status >= 0)
345				status = -EFAULT;
346		if (status < 0)
347			break;
348	} while (count);
349	*ppos = pos;
350	/*
351	 * No need to use i_size_read() here, the i_size
352	 * cannot change under us because we hold i_mutex.
353	 */
354	if (pos > inode->i_size) {
355		i_size_write(inode, pos);
356		mark_inode_dirty(inode);
357	}
358
359	return written ? written : status;
360}
361
362ssize_t
363xip_file_write(struct file *filp, const char __user *buf, size_t len,
364	       loff_t *ppos)
365{
366	struct address_space *mapping = filp->f_mapping;
367	struct inode *inode = mapping->host;
368	size_t count;
369	loff_t pos;
370	ssize_t ret;
371
372	mutex_lock(&inode->i_mutex);
373
374	if (!access_ok(VERIFY_READ, buf, len)) {
375		ret=-EFAULT;
376		goto out_up;
377	}
378
379	pos = *ppos;
380	count = len;
381
382	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
383
384	/* We can write back this queue in page reclaim */
385	current->backing_dev_info = mapping->backing_dev_info;
386
387	ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
388	if (ret)
389		goto out_backing;
390	if (count == 0)
391		goto out_backing;
392
393	ret = remove_suid(filp->f_path.dentry);
394	if (ret)
395		goto out_backing;
396
397	file_update_time(filp);
398
399	ret = __xip_file_write (filp, buf, count, pos, ppos);
400
401 out_backing:
402	current->backing_dev_info = NULL;
403 out_up:
404	mutex_unlock(&inode->i_mutex);
405	return ret;
406}
407EXPORT_SYMBOL_GPL(xip_file_write);
408
409/*
410 * truncate a page used for execute in place
411 * functionality is analog to block_truncate_page but does use get_xip_page
412 * to get the page instead of page cache
413 */
414int
415xip_truncate_page(struct address_space *mapping, loff_t from)
416{
417	pgoff_t index = from >> PAGE_CACHE_SHIFT;
418	unsigned offset = from & (PAGE_CACHE_SIZE-1);
419	unsigned blocksize;
420	unsigned length;
421	struct page *page;
422
423	BUG_ON(!mapping->a_ops->get_xip_page);
424
425	blocksize = 1 << mapping->host->i_blkbits;
426	length = offset & (blocksize - 1);
427
428	/* Block boundary? Nothing to do */
429	if (!length)
430		return 0;
431
432	length = blocksize - length;
433
434	page = mapping->a_ops->get_xip_page(mapping,
435					    index*(PAGE_SIZE/512), 0);
436	if (!page)
437		return -ENOMEM;
438	if (unlikely(IS_ERR(page))) {
439		if (PTR_ERR(page) == -ENODATA)
440			/* Hole? No need to truncate */
441			return 0;
442		else
443			return PTR_ERR(page);
444	}
445	zero_user_page(page, offset, length, KM_USER0);
446	return 0;
447}
448EXPORT_SYMBOL_GPL(xip_truncate_page);
449