xref: /openbmc/linux/mm/mincore.c (revision 49b06385)
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 #include "swap.h"
24 
mincore_hugetlb(pte_t * pte,unsigned long hmask,unsigned long addr,unsigned long end,struct mm_walk * walk)25 static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
26 			unsigned long end, struct mm_walk *walk)
27 {
28 #ifdef CONFIG_HUGETLB_PAGE
29 	unsigned char present;
30 	unsigned char *vec = walk->private;
31 
32 	/*
33 	 * Hugepages under user process are always in RAM and never
34 	 * swapped out, but theoretically it needs to be checked.
35 	 */
36 	present = pte && !huge_pte_none_mostly(huge_ptep_get(pte));
37 	for (; addr != end; vec++, addr += PAGE_SIZE)
38 		*vec = present;
39 	walk->private = vec;
40 #else
41 	BUG();
42 #endif
43 	return 0;
44 }
45 
46 /*
47  * Later we can get more picky about what "in core" means precisely.
48  * For now, simply check to see if the page is in the page cache,
49  * and is up to date; i.e. that no page-in operation would be required
50  * at this time if an application were to map and access this page.
51  */
mincore_page(struct address_space * mapping,pgoff_t index)52 static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
53 {
54 	unsigned char present = 0;
55 	struct folio *folio;
56 
57 	/*
58 	 * When tmpfs swaps out a page from a file, any process mapping that
59 	 * file will not get a swp_entry_t in its pte, but rather it is like
60 	 * any other file mapping (ie. marked !present and faulted in with
61 	 * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
62 	 */
63 	folio = filemap_get_incore_folio(mapping, index);
64 	if (!IS_ERR(folio)) {
65 		present = folio_test_uptodate(folio);
66 		folio_put(folio);
67 	}
68 
69 	return present;
70 }
71 
__mincore_unmapped_range(unsigned long addr,unsigned long end,struct vm_area_struct * vma,unsigned char * vec)72 static int __mincore_unmapped_range(unsigned long addr, unsigned long end,
73 				struct vm_area_struct *vma, unsigned char *vec)
74 {
75 	unsigned long nr = (end - addr) >> PAGE_SHIFT;
76 	int i;
77 
78 	if (vma->vm_file) {
79 		pgoff_t pgoff;
80 
81 		pgoff = linear_page_index(vma, addr);
82 		for (i = 0; i < nr; i++, pgoff++)
83 			vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
84 	} else {
85 		for (i = 0; i < nr; i++)
86 			vec[i] = 0;
87 	}
88 	return nr;
89 }
90 
mincore_unmapped_range(unsigned long addr,unsigned long end,__always_unused int depth,struct mm_walk * walk)91 static int mincore_unmapped_range(unsigned long addr, unsigned long end,
92 				   __always_unused int depth,
93 				   struct mm_walk *walk)
94 {
95 	walk->private += __mincore_unmapped_range(addr, end,
96 						  walk->vma, walk->private);
97 	return 0;
98 }
99 
mincore_pte_range(pmd_t * pmd,unsigned long addr,unsigned long end,struct mm_walk * walk)100 static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
101 			struct mm_walk *walk)
102 {
103 	spinlock_t *ptl;
104 	struct vm_area_struct *vma = walk->vma;
105 	pte_t *ptep;
106 	unsigned char *vec = walk->private;
107 	int nr = (end - addr) >> PAGE_SHIFT;
108 
109 	ptl = pmd_trans_huge_lock(pmd, vma);
110 	if (ptl) {
111 		memset(vec, 1, nr);
112 		spin_unlock(ptl);
113 		goto out;
114 	}
115 
116 	ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
117 	if (!ptep) {
118 		walk->action = ACTION_AGAIN;
119 		return 0;
120 	}
121 	for (; addr != end; ptep++, addr += PAGE_SIZE) {
122 		pte_t pte = ptep_get(ptep);
123 
124 		/* We need to do cache lookup too for pte markers */
125 		if (pte_none_mostly(pte))
126 			__mincore_unmapped_range(addr, addr + PAGE_SIZE,
127 						 vma, vec);
128 		else if (pte_present(pte))
129 			*vec = 1;
130 		else { /* pte is a swap entry */
131 			swp_entry_t entry = pte_to_swp_entry(pte);
132 
133 			if (non_swap_entry(entry)) {
134 				/*
135 				 * migration or hwpoison entries are always
136 				 * uptodate
137 				 */
138 				*vec = 1;
139 			} else {
140 #ifdef CONFIG_SWAP
141 				*vec = mincore_page(swap_address_space(entry),
142 						    swp_offset(entry));
143 #else
144 				WARN_ON(1);
145 				*vec = 1;
146 #endif
147 			}
148 		}
149 		vec++;
150 	}
151 	pte_unmap_unlock(ptep - 1, ptl);
152 out:
153 	walk->private += nr;
154 	cond_resched();
155 	return 0;
156 }
157 
can_do_mincore(struct vm_area_struct * vma)158 static inline bool can_do_mincore(struct vm_area_struct *vma)
159 {
160 	if (vma_is_anonymous(vma))
161 		return true;
162 	if (!vma->vm_file)
163 		return false;
164 	/*
165 	 * Reveal pagecache information only for non-anonymous mappings that
166 	 * correspond to the files the calling process could (if tried) open
167 	 * for writing; otherwise we'd be including shared non-exclusive
168 	 * mappings, which opens a side channel.
169 	 */
170 	return inode_owner_or_capable(&nop_mnt_idmap,
171 				      file_inode(vma->vm_file)) ||
172 	       file_permission(vma->vm_file, MAY_WRITE) == 0;
173 }
174 
175 static const struct mm_walk_ops mincore_walk_ops = {
176 	.pmd_entry		= mincore_pte_range,
177 	.pte_hole		= mincore_unmapped_range,
178 	.hugetlb_entry		= mincore_hugetlb,
179 	.walk_lock		= PGWALK_RDLOCK,
180 };
181 
182 /*
183  * Do a chunk of "sys_mincore()". We've already checked
184  * all the arguments, we hold the mmap semaphore: we should
185  * just return the amount of info we're asked for.
186  */
do_mincore(unsigned long addr,unsigned long pages,unsigned char * vec)187 static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
188 {
189 	struct vm_area_struct *vma;
190 	unsigned long end;
191 	int err;
192 
193 	vma = vma_lookup(current->mm, addr);
194 	if (!vma)
195 		return -ENOMEM;
196 	end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
197 	if (!can_do_mincore(vma)) {
198 		unsigned long pages = DIV_ROUND_UP(end - addr, PAGE_SIZE);
199 		memset(vec, 1, pages);
200 		return pages;
201 	}
202 	err = walk_page_range(vma->vm_mm, addr, end, &mincore_walk_ops, vec);
203 	if (err < 0)
204 		return err;
205 	return (end - addr) >> PAGE_SHIFT;
206 }
207 
208 /*
209  * The mincore(2) system call.
210  *
211  * mincore() returns the memory residency status of the pages in the
212  * current process's address space specified by [addr, addr + len).
213  * The status is returned in a vector of bytes.  The least significant
214  * bit of each byte is 1 if the referenced page is in memory, otherwise
215  * it is zero.
216  *
217  * Because the status of a page can change after mincore() checks it
218  * but before it returns to the application, the returned vector may
219  * contain stale information.  Only locked pages are guaranteed to
220  * remain in memory.
221  *
222  * return values:
223  *  zero    - success
224  *  -EFAULT - vec points to an illegal address
225  *  -EINVAL - addr is not a multiple of PAGE_SIZE
226  *  -ENOMEM - Addresses in the range [addr, addr + len] are
227  *		invalid for the address space of this process, or
228  *		specify one or more pages which are not currently
229  *		mapped
230  *  -EAGAIN - A kernel resource was temporarily unavailable.
231  */
SYSCALL_DEFINE3(mincore,unsigned long,start,size_t,len,unsigned char __user *,vec)232 SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
233 		unsigned char __user *, vec)
234 {
235 	long retval;
236 	unsigned long pages;
237 	unsigned char *tmp;
238 
239 	start = untagged_addr(start);
240 
241 	/* Check the start address: needs to be page-aligned.. */
242 	if (start & ~PAGE_MASK)
243 		return -EINVAL;
244 
245 	/* ..and we need to be passed a valid user-space range */
246 	if (!access_ok((void __user *) start, len))
247 		return -ENOMEM;
248 
249 	/* This also avoids any overflows on PAGE_ALIGN */
250 	pages = len >> PAGE_SHIFT;
251 	pages += (offset_in_page(len)) != 0;
252 
253 	if (!access_ok(vec, pages))
254 		return -EFAULT;
255 
256 	tmp = (void *) __get_free_page(GFP_USER);
257 	if (!tmp)
258 		return -EAGAIN;
259 
260 	retval = 0;
261 	while (pages) {
262 		/*
263 		 * Do at most PAGE_SIZE entries per iteration, due to
264 		 * the temporary buffer size.
265 		 */
266 		mmap_read_lock(current->mm);
267 		retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
268 		mmap_read_unlock(current->mm);
269 
270 		if (retval <= 0)
271 			break;
272 		if (copy_to_user(vec, tmp, retval)) {
273 			retval = -EFAULT;
274 			break;
275 		}
276 		pages -= retval;
277 		vec += retval;
278 		start += retval << PAGE_SHIFT;
279 		retval = 0;
280 	}
281 	free_page((unsigned long) tmp);
282 	return retval;
283 }
284