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 #include "internal.h" 25 26 static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr, 27 unsigned long end, struct mm_walk *walk) 28 { 29 #ifdef CONFIG_HUGETLB_PAGE 30 unsigned char present; 31 unsigned char *vec = walk->private; 32 spinlock_t *ptl; 33 34 ptl = huge_pte_lock(hstate_vma(walk->vma), walk->mm, pte); 35 /* 36 * Hugepages under user process are always in RAM and never 37 * swapped out, but theoretically it needs to be checked. 38 */ 39 present = pte && !huge_pte_none_mostly(huge_ptep_get(walk->mm, addr, pte)); 40 for (; addr != end; vec++, addr += PAGE_SIZE) 41 *vec = present; 42 walk->private = vec; 43 spin_unlock(ptl); 44 #else 45 BUG(); 46 #endif 47 return 0; 48 } 49 50 static unsigned char mincore_swap(swp_entry_t entry, bool shmem) 51 { 52 struct swap_info_struct *si; 53 struct folio *folio = NULL; 54 unsigned char present = 0; 55 56 if (!IS_ENABLED(CONFIG_SWAP)) { 57 WARN_ON(1); 58 return 0; 59 } 60 61 /* 62 * Shmem mapping may contain swapin error entries, which are 63 * absent. Page table may contain migration or hwpoison 64 * entries which are always uptodate. 65 */ 66 if (non_swap_entry(entry)) 67 return !shmem; 68 69 /* 70 * Shmem mapping lookup is lockless, so we need to grab the swap 71 * device. mincore page table walk locks the PTL, and the swap 72 * device is stable, avoid touching the si for better performance. 73 */ 74 if (shmem) { 75 si = get_swap_device(entry); 76 if (!si) 77 return 0; 78 } 79 folio = filemap_get_entry(swap_address_space(entry), 80 swap_cache_index(entry)); 81 if (shmem) 82 put_swap_device(si); 83 /* The swap cache space contains either folio, shadow or NULL */ 84 if (folio && !xa_is_value(folio)) { 85 present = folio_test_uptodate(folio); 86 folio_put(folio); 87 } 88 89 return present; 90 } 91 92 /* 93 * Later we can get more picky about what "in core" means precisely. 94 * For now, simply check to see if the page is in the page cache, 95 * and is up to date; i.e. that no page-in operation would be required 96 * at this time if an application were to map and access this page. 97 */ 98 static unsigned char mincore_page(struct address_space *mapping, pgoff_t index) 99 { 100 unsigned char present = 0; 101 struct folio *folio; 102 103 /* 104 * When tmpfs swaps out a page from a file, any process mapping that 105 * file will not get a swp_entry_t in its pte, but rather it is like 106 * any other file mapping (ie. marked !present and faulted in with 107 * tmpfs's .fault). So swapped out tmpfs mappings are tested here. 108 */ 109 folio = filemap_get_entry(mapping, index); 110 if (folio) { 111 if (xa_is_value(folio)) { 112 if (shmem_mapping(mapping)) 113 return mincore_swap(radix_to_swp_entry(folio), 114 true); 115 else 116 return 0; 117 } 118 present = folio_test_uptodate(folio); 119 folio_put(folio); 120 } 121 122 return present; 123 } 124 125 static int __mincore_unmapped_range(unsigned long addr, unsigned long end, 126 struct vm_area_struct *vma, unsigned char *vec) 127 { 128 unsigned long nr = (end - addr) >> PAGE_SHIFT; 129 int i; 130 131 if (vma->vm_file) { 132 pgoff_t pgoff; 133 134 pgoff = linear_page_index(vma, addr); 135 for (i = 0; i < nr; i++, pgoff++) 136 vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff); 137 } else { 138 for (i = 0; i < nr; i++) 139 vec[i] = 0; 140 } 141 return nr; 142 } 143 144 static int mincore_unmapped_range(unsigned long addr, unsigned long end, 145 __always_unused int depth, 146 struct mm_walk *walk) 147 { 148 walk->private += __mincore_unmapped_range(addr, end, 149 walk->vma, walk->private); 150 return 0; 151 } 152 153 static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, 154 struct mm_walk *walk) 155 { 156 spinlock_t *ptl; 157 struct vm_area_struct *vma = walk->vma; 158 pte_t *ptep; 159 unsigned char *vec = walk->private; 160 int nr = (end - addr) >> PAGE_SHIFT; 161 int step, i; 162 163 ptl = pmd_trans_huge_lock(pmd, vma); 164 if (ptl) { 165 memset(vec, 1, nr); 166 spin_unlock(ptl); 167 goto out; 168 } 169 170 ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); 171 if (!ptep) { 172 walk->action = ACTION_AGAIN; 173 return 0; 174 } 175 for (; addr != end; ptep += step, addr += step * PAGE_SIZE) { 176 pte_t pte = ptep_get(ptep); 177 178 step = 1; 179 /* We need to do cache lookup too for pte markers */ 180 if (pte_none_mostly(pte)) 181 __mincore_unmapped_range(addr, addr + PAGE_SIZE, 182 vma, vec); 183 else if (pte_present(pte)) { 184 unsigned int batch = pte_batch_hint(ptep, pte); 185 186 if (batch > 1) { 187 unsigned int max_nr = (end - addr) >> PAGE_SHIFT; 188 189 step = min_t(unsigned int, batch, max_nr); 190 } 191 192 for (i = 0; i < step; i++) 193 vec[i] = 1; 194 } else { /* pte is a swap entry */ 195 *vec = mincore_swap(pte_to_swp_entry(pte), false); 196 } 197 vec += step; 198 } 199 pte_unmap_unlock(ptep - 1, ptl); 200 out: 201 walk->private += nr; 202 cond_resched(); 203 return 0; 204 } 205 206 static inline bool can_do_mincore(struct vm_area_struct *vma) 207 { 208 if (vma_is_anonymous(vma)) 209 return true; 210 if (!vma->vm_file) 211 return false; 212 /* 213 * Reveal pagecache information only for non-anonymous mappings that 214 * correspond to the files the calling process could (if tried) open 215 * for writing; otherwise we'd be including shared non-exclusive 216 * mappings, which opens a side channel. 217 */ 218 return inode_owner_or_capable(&nop_mnt_idmap, 219 file_inode(vma->vm_file)) || 220 file_permission(vma->vm_file, MAY_WRITE) == 0; 221 } 222 223 static const struct mm_walk_ops mincore_walk_ops = { 224 .pmd_entry = mincore_pte_range, 225 .pte_hole = mincore_unmapped_range, 226 .hugetlb_entry = mincore_hugetlb, 227 .walk_lock = PGWALK_RDLOCK, 228 }; 229 230 /* 231 * Do a chunk of "sys_mincore()". We've already checked 232 * all the arguments, we hold the mmap semaphore: we should 233 * just return the amount of info we're asked for. 234 */ 235 static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec) 236 { 237 struct vm_area_struct *vma; 238 unsigned long end; 239 int err; 240 241 vma = vma_lookup(current->mm, addr); 242 if (!vma) 243 return -ENOMEM; 244 end = min(vma->vm_end, addr + (pages << PAGE_SHIFT)); 245 if (!can_do_mincore(vma)) { 246 unsigned long pages = DIV_ROUND_UP(end - addr, PAGE_SIZE); 247 memset(vec, 1, pages); 248 return pages; 249 } 250 err = walk_page_range(vma->vm_mm, addr, end, &mincore_walk_ops, vec); 251 if (err < 0) 252 return err; 253 return (end - addr) >> PAGE_SHIFT; 254 } 255 256 /* 257 * The mincore(2) system call. 258 * 259 * mincore() returns the memory residency status of the pages in the 260 * current process's address space specified by [addr, addr + len). 261 * The status is returned in a vector of bytes. The least significant 262 * bit of each byte is 1 if the referenced page is in memory, otherwise 263 * it is zero. 264 * 265 * Because the status of a page can change after mincore() checks it 266 * but before it returns to the application, the returned vector may 267 * contain stale information. Only locked pages are guaranteed to 268 * remain in memory. 269 * 270 * return values: 271 * zero - success 272 * -EFAULT - vec points to an illegal address 273 * -EINVAL - addr is not a multiple of PAGE_SIZE 274 * -ENOMEM - Addresses in the range [addr, addr + len] are 275 * invalid for the address space of this process, or 276 * specify one or more pages which are not currently 277 * mapped 278 * -EAGAIN - A kernel resource was temporarily unavailable. 279 */ 280 SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len, 281 unsigned char __user *, vec) 282 { 283 long retval; 284 unsigned long pages; 285 unsigned char *tmp; 286 287 start = untagged_addr(start); 288 289 /* Check the start address: needs to be page-aligned.. */ 290 if (unlikely(start & ~PAGE_MASK)) 291 return -EINVAL; 292 293 /* ..and we need to be passed a valid user-space range */ 294 if (!access_ok((void __user *) start, len)) 295 return -ENOMEM; 296 297 /* This also avoids any overflows on PAGE_ALIGN */ 298 pages = len >> PAGE_SHIFT; 299 pages += (offset_in_page(len)) != 0; 300 301 if (!access_ok(vec, pages)) 302 return -EFAULT; 303 304 tmp = (void *) __get_free_page(GFP_USER); 305 if (!tmp) 306 return -EAGAIN; 307 308 retval = 0; 309 while (pages) { 310 /* 311 * Do at most PAGE_SIZE entries per iteration, due to 312 * the temporary buffer size. 313 */ 314 mmap_read_lock(current->mm); 315 retval = do_mincore(start, min(pages, PAGE_SIZE), tmp); 316 mmap_read_unlock(current->mm); 317 318 if (retval <= 0) 319 break; 320 if (copy_to_user(vec, tmp, retval)) { 321 retval = -EFAULT; 322 break; 323 } 324 pages -= retval; 325 vec += retval; 326 start += retval << PAGE_SHIFT; 327 retval = 0; 328 } 329 free_page((unsigned long) tmp); 330 return retval; 331 } 332