xref: /openbmc/linux/mm/mincore.c (revision 67e2fae3)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *	linux/mm/mincore.c
4  *
5  * Copyright (C) 1994-2006  Linus Torvalds
6  */
7 
8 /*
9  * The mincore() system call.
10  */
11 #include <linux/pagemap.h>
12 #include <linux/gfp.h>
13 #include <linux/pagewalk.h>
14 #include <linux/mman.h>
15 #include <linux/syscalls.h>
16 #include <linux/swap.h>
17 #include <linux/swapops.h>
18 #include <linux/shmem_fs.h>
19 #include <linux/hugetlb.h>
20 #include <linux/pgtable.h>
21 
22 #include <linux/uaccess.h>
23 
24 static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
25 			unsigned long end, struct mm_walk *walk)
26 {
27 #ifdef CONFIG_HUGETLB_PAGE
28 	unsigned char present;
29 	unsigned char *vec = walk->private;
30 
31 	/*
32 	 * Hugepages under user process are always in RAM and never
33 	 * swapped out, but theoretically it needs to be checked.
34 	 */
35 	present = pte && !huge_pte_none(huge_ptep_get(pte));
36 	for (; addr != end; vec++, addr += PAGE_SIZE)
37 		*vec = present;
38 	walk->private = vec;
39 #else
40 	BUG();
41 #endif
42 	return 0;
43 }
44 
45 /*
46  * Later we can get more picky about what "in core" means precisely.
47  * For now, simply check to see if the page is in the page cache,
48  * and is up to date; i.e. that no page-in operation would be required
49  * at this time if an application were to map and access this page.
50  */
51 static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
52 {
53 	unsigned char present = 0;
54 	struct page *page;
55 
56 	/*
57 	 * When tmpfs swaps out a page from a file, any process mapping that
58 	 * file will not get a swp_entry_t in its pte, but rather it is like
59 	 * any other file mapping (ie. marked !present and faulted in with
60 	 * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
61 	 */
62 #ifdef CONFIG_SWAP
63 	if (shmem_mapping(mapping)) {
64 		page = find_get_entry(mapping, pgoff);
65 		/*
66 		 * shmem/tmpfs may return swap: account for swapcache
67 		 * page too.
68 		 */
69 		if (xa_is_value(page)) {
70 			swp_entry_t swp = radix_to_swp_entry(page);
71 			struct swap_info_struct *si;
72 
73 			/* Prevent swap device to being swapoff under us */
74 			si = get_swap_device(swp);
75 			if (si) {
76 				page = find_get_page(swap_address_space(swp),
77 						     swp_offset(swp));
78 				put_swap_device(si);
79 			} else
80 				page = NULL;
81 		}
82 	} else
83 		page = find_get_page(mapping, pgoff);
84 #else
85 	page = find_get_page(mapping, pgoff);
86 #endif
87 	if (page) {
88 		present = PageUptodate(page);
89 		put_page(page);
90 	}
91 
92 	return present;
93 }
94 
95 static int __mincore_unmapped_range(unsigned long addr, unsigned long end,
96 				struct vm_area_struct *vma, unsigned char *vec)
97 {
98 	unsigned long nr = (end - addr) >> PAGE_SHIFT;
99 	int i;
100 
101 	if (vma->vm_file) {
102 		pgoff_t pgoff;
103 
104 		pgoff = linear_page_index(vma, addr);
105 		for (i = 0; i < nr; i++, pgoff++)
106 			vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
107 	} else {
108 		for (i = 0; i < nr; i++)
109 			vec[i] = 0;
110 	}
111 	return nr;
112 }
113 
114 static int mincore_unmapped_range(unsigned long addr, unsigned long end,
115 				   __always_unused int depth,
116 				   struct mm_walk *walk)
117 {
118 	walk->private += __mincore_unmapped_range(addr, end,
119 						  walk->vma, walk->private);
120 	return 0;
121 }
122 
123 static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
124 			struct mm_walk *walk)
125 {
126 	spinlock_t *ptl;
127 	struct vm_area_struct *vma = walk->vma;
128 	pte_t *ptep;
129 	unsigned char *vec = walk->private;
130 	int nr = (end - addr) >> PAGE_SHIFT;
131 
132 	ptl = pmd_trans_huge_lock(pmd, vma);
133 	if (ptl) {
134 		memset(vec, 1, nr);
135 		spin_unlock(ptl);
136 		goto out;
137 	}
138 
139 	if (pmd_trans_unstable(pmd)) {
140 		__mincore_unmapped_range(addr, end, vma, vec);
141 		goto out;
142 	}
143 
144 	ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
145 	for (; addr != end; ptep++, addr += PAGE_SIZE) {
146 		pte_t pte = *ptep;
147 
148 		if (pte_none(pte))
149 			__mincore_unmapped_range(addr, addr + PAGE_SIZE,
150 						 vma, vec);
151 		else if (pte_present(pte))
152 			*vec = 1;
153 		else { /* pte is a swap entry */
154 			swp_entry_t entry = pte_to_swp_entry(pte);
155 
156 			if (non_swap_entry(entry)) {
157 				/*
158 				 * migration or hwpoison entries are always
159 				 * uptodate
160 				 */
161 				*vec = 1;
162 			} else {
163 #ifdef CONFIG_SWAP
164 				*vec = mincore_page(swap_address_space(entry),
165 						    swp_offset(entry));
166 #else
167 				WARN_ON(1);
168 				*vec = 1;
169 #endif
170 			}
171 		}
172 		vec++;
173 	}
174 	pte_unmap_unlock(ptep - 1, ptl);
175 out:
176 	walk->private += nr;
177 	cond_resched();
178 	return 0;
179 }
180 
181 static inline bool can_do_mincore(struct vm_area_struct *vma)
182 {
183 	if (vma_is_anonymous(vma))
184 		return true;
185 	if (!vma->vm_file)
186 		return false;
187 	/*
188 	 * Reveal pagecache information only for non-anonymous mappings that
189 	 * correspond to the files the calling process could (if tried) open
190 	 * for writing; otherwise we'd be including shared non-exclusive
191 	 * mappings, which opens a side channel.
192 	 */
193 	return inode_owner_or_capable(file_inode(vma->vm_file)) ||
194 		inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0;
195 }
196 
197 static const struct mm_walk_ops mincore_walk_ops = {
198 	.pmd_entry		= mincore_pte_range,
199 	.pte_hole		= mincore_unmapped_range,
200 	.hugetlb_entry		= mincore_hugetlb,
201 };
202 
203 /*
204  * Do a chunk of "sys_mincore()". We've already checked
205  * all the arguments, we hold the mmap semaphore: we should
206  * just return the amount of info we're asked for.
207  */
208 static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
209 {
210 	struct vm_area_struct *vma;
211 	unsigned long end;
212 	int err;
213 
214 	vma = find_vma(current->mm, addr);
215 	if (!vma || addr < vma->vm_start)
216 		return -ENOMEM;
217 	end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
218 	if (!can_do_mincore(vma)) {
219 		unsigned long pages = DIV_ROUND_UP(end - addr, PAGE_SIZE);
220 		memset(vec, 1, pages);
221 		return pages;
222 	}
223 	err = walk_page_range(vma->vm_mm, addr, end, &mincore_walk_ops, vec);
224 	if (err < 0)
225 		return err;
226 	return (end - addr) >> PAGE_SHIFT;
227 }
228 
229 /*
230  * The mincore(2) system call.
231  *
232  * mincore() returns the memory residency status of the pages in the
233  * current process's address space specified by [addr, addr + len).
234  * The status is returned in a vector of bytes.  The least significant
235  * bit of each byte is 1 if the referenced page is in memory, otherwise
236  * it is zero.
237  *
238  * Because the status of a page can change after mincore() checks it
239  * but before it returns to the application, the returned vector may
240  * contain stale information.  Only locked pages are guaranteed to
241  * remain in memory.
242  *
243  * return values:
244  *  zero    - success
245  *  -EFAULT - vec points to an illegal address
246  *  -EINVAL - addr is not a multiple of PAGE_SIZE
247  *  -ENOMEM - Addresses in the range [addr, addr + len] are
248  *		invalid for the address space of this process, or
249  *		specify one or more pages which are not currently
250  *		mapped
251  *  -EAGAIN - A kernel resource was temporarily unavailable.
252  */
253 SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
254 		unsigned char __user *, vec)
255 {
256 	long retval;
257 	unsigned long pages;
258 	unsigned char *tmp;
259 
260 	start = untagged_addr(start);
261 
262 	/* Check the start address: needs to be page-aligned.. */
263 	if (start & ~PAGE_MASK)
264 		return -EINVAL;
265 
266 	/* ..and we need to be passed a valid user-space range */
267 	if (!access_ok((void __user *) start, len))
268 		return -ENOMEM;
269 
270 	/* This also avoids any overflows on PAGE_ALIGN */
271 	pages = len >> PAGE_SHIFT;
272 	pages += (offset_in_page(len)) != 0;
273 
274 	if (!access_ok(vec, pages))
275 		return -EFAULT;
276 
277 	tmp = (void *) __get_free_page(GFP_USER);
278 	if (!tmp)
279 		return -EAGAIN;
280 
281 	retval = 0;
282 	while (pages) {
283 		/*
284 		 * Do at most PAGE_SIZE entries per iteration, due to
285 		 * the temporary buffer size.
286 		 */
287 		mmap_read_lock(current->mm);
288 		retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
289 		mmap_read_unlock(current->mm);
290 
291 		if (retval <= 0)
292 			break;
293 		if (copy_to_user(vec, tmp, retval)) {
294 			retval = -EFAULT;
295 			break;
296 		}
297 		pages -= retval;
298 		vec += retval;
299 		start += retval << PAGE_SHIFT;
300 		retval = 0;
301 	}
302 	free_page((unsigned long) tmp);
303 	return retval;
304 }
305