On Tue, Oct 17, 2023 at 12:40 PM kernel test robot <lkp@xxxxxxxxx> wrote: > > Hi Suren, > > kernel test robot noticed the following build warnings: > > [auto build test WARNING on akpm-mm/mm-everything] > [also build test WARNING on next-20231017] > [cannot apply to linus/master v6.6-rc6] > [If your patch is applied to the wrong git tree, kindly drop us a note. > And when submitting patch, we suggest to use '--base' as documented in > https://git-scm.com/docs/git-format-patch#_base_tree_information] > > url: https://github.com/intel-lab-lkp/linux/commits/Suren-Baghdasaryan/mm-rmap-support-move-to-different-root-anon_vma-in-folio_move_anon_rmap/20231009-144552 > base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything > patch link: https://lore.kernel.org/r/20231009064230.2952396-3-surenb%40google.com > patch subject: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI > config: i386-randconfig-141-20231017 (https://download.01.org/0day-ci/archive/20231018/202310180338.zTpcYECK-lkp@xxxxxxxxx/config) > compiler: gcc-12 (Debian 12.2.0-14) 12.2.0 > reproduce: (https://download.01.org/0day-ci/archive/20231018/202310180338.zTpcYECK-lkp@xxxxxxxxx/reproduce) > > If you fix the issue in a separate patch/commit (i.e. not just a new version of > the same patch/commit), kindly add following tags > | Reported-by: kernel test robot <lkp@xxxxxxxxx> > | Closes: https://lore.kernel.org/oe-kbuild-all/202310180338.zTpcYECK-lkp@xxxxxxxxx/ > > smatch warnings: > mm/userfaultfd.c:1380 remap_pages() warn: unsigned 'src_start + len - src_addr' is never less than zero. Hmm. I think this warning is correct only when CONFIG_TRANSPARENT_HUGEPAGE=n. I guess I'll have to add an "ifdef CONFIG_TRANSPARENT_HUGEPAGE" here after all, which lets us move these checks before locking PTL. > > vim +1380 mm/userfaultfd.c > > 1195 > 1196 /** > 1197 * remap_pages - remap arbitrary anonymous pages of an existing vma > 1198 * @dst_start: start of the destination virtual memory range > 1199 * @src_start: start of the source virtual memory range > 1200 * @len: length of the virtual memory range > 1201 * > 1202 * remap_pages() remaps arbitrary anonymous pages atomically in zero > 1203 * copy. It only works on non shared anonymous pages because those can > 1204 * be relocated without generating non linear anon_vmas in the rmap > 1205 * code. > 1206 * > 1207 * It provides a zero copy mechanism to handle userspace page faults. > 1208 * The source vma pages should have mapcount == 1, which can be > 1209 * enforced by using madvise(MADV_DONTFORK) on src vma. > 1210 * > 1211 * The thread receiving the page during the userland page fault > 1212 * will receive the faulting page in the source vma through the network, > 1213 * storage or any other I/O device (MADV_DONTFORK in the source vma > 1214 * avoids remap_pages() to fail with -EBUSY if the process forks before > 1215 * remap_pages() is called), then it will call remap_pages() to map the > 1216 * page in the faulting address in the destination vma. > 1217 * > 1218 * This userfaultfd command works purely via pagetables, so it's the > 1219 * most efficient way to move physical non shared anonymous pages > 1220 * across different virtual addresses. Unlike mremap()/mmap()/munmap() > 1221 * it does not create any new vmas. The mapping in the destination > 1222 * address is atomic. > 1223 * > 1224 * It only works if the vma protection bits are identical from the > 1225 * source and destination vma. > 1226 * > 1227 * It can remap non shared anonymous pages within the same vma too. > 1228 * > 1229 * If the source virtual memory range has any unmapped holes, or if > 1230 * the destination virtual memory range is not a whole unmapped hole, > 1231 * remap_pages() will fail respectively with -ENOENT or -EEXIST. This > 1232 * provides a very strict behavior to avoid any chance of memory > 1233 * corruption going unnoticed if there are userland race conditions. > 1234 * Only one thread should resolve the userland page fault at any given > 1235 * time for any given faulting address. This means that if two threads > 1236 * try to both call remap_pages() on the same destination address at the > 1237 * same time, the second thread will get an explicit error from this > 1238 * command. > 1239 * > 1240 * The command retval will return "len" is successful. The command > 1241 * however can be interrupted by fatal signals or errors. If > 1242 * interrupted it will return the number of bytes successfully > 1243 * remapped before the interruption if any, or the negative error if > 1244 * none. It will never return zero. Either it will return an error or > 1245 * an amount of bytes successfully moved. If the retval reports a > 1246 * "short" remap, the remap_pages() command should be repeated by > 1247 * userland with src+retval, dst+reval, len-retval if it wants to know > 1248 * about the error that interrupted it. > 1249 * > 1250 * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to > 1251 * prevent -ENOENT errors to materialize if there are holes in the > 1252 * source virtual range that is being remapped. The holes will be > 1253 * accounted as successfully remapped in the retval of the > 1254 * command. This is mostly useful to remap hugepage naturally aligned > 1255 * virtual regions without knowing if there are transparent hugepage > 1256 * in the regions or not, but preventing the risk of having to split > 1257 * the hugepmd during the remap. > 1258 * > 1259 * If there's any rmap walk that is taking the anon_vma locks without > 1260 * first obtaining the folio lock (the only current instance is > 1261 * folio_referenced), they will have to verify if the folio->mapping > 1262 * has changed after taking the anon_vma lock. If it changed they > 1263 * should release the lock and retry obtaining a new anon_vma, because > 1264 * it means the anon_vma was changed by remap_pages() before the lock > 1265 * could be obtained. This is the only additional complexity added to > 1266 * the rmap code to provide this anonymous page remapping functionality. > 1267 */ > 1268 ssize_t remap_pages(struct mm_struct *dst_mm, struct mm_struct *src_mm, > 1269 unsigned long dst_start, unsigned long src_start, > 1270 unsigned long len, __u64 mode) > 1271 { > 1272 struct vm_area_struct *src_vma, *dst_vma; > 1273 unsigned long src_addr, dst_addr; > 1274 pmd_t *src_pmd, *dst_pmd; > 1275 long err = -EINVAL; > 1276 ssize_t moved = 0; > 1277 > 1278 /* > 1279 * Sanitize the command parameters: > 1280 */ > 1281 BUG_ON(src_start & ~PAGE_MASK); > 1282 BUG_ON(dst_start & ~PAGE_MASK); > 1283 BUG_ON(len & ~PAGE_MASK); > 1284 > 1285 /* Does the address range wrap, or is the span zero-sized? */ > 1286 BUG_ON(src_start + len <= src_start); > 1287 BUG_ON(dst_start + len <= dst_start); > 1288 > 1289 /* > 1290 * Because these are read sempahores there's no risk of lock > 1291 * inversion. > 1292 */ > 1293 mmap_read_lock(dst_mm); > 1294 if (dst_mm != src_mm) > 1295 mmap_read_lock(src_mm); > 1296 > 1297 /* > 1298 * Make sure the vma is not shared, that the src and dst remap > 1299 * ranges are both valid and fully within a single existing > 1300 * vma. > 1301 */ > 1302 src_vma = find_vma(src_mm, src_start); > 1303 if (!src_vma || (src_vma->vm_flags & VM_SHARED)) > 1304 goto out; > 1305 if (src_start < src_vma->vm_start || > 1306 src_start + len > src_vma->vm_end) > 1307 goto out; > 1308 > 1309 dst_vma = find_vma(dst_mm, dst_start); > 1310 if (!dst_vma || (dst_vma->vm_flags & VM_SHARED)) > 1311 goto out; > 1312 if (dst_start < dst_vma->vm_start || > 1313 dst_start + len > dst_vma->vm_end) > 1314 goto out; > 1315 > 1316 err = validate_remap_areas(src_vma, dst_vma); > 1317 if (err) > 1318 goto out; > 1319 > 1320 for (src_addr = src_start, dst_addr = dst_start; > 1321 src_addr < src_start + len;) { > 1322 spinlock_t *ptl; > 1323 pmd_t dst_pmdval; > 1324 unsigned long step_size; > 1325 > 1326 BUG_ON(dst_addr >= dst_start + len); > 1327 /* > 1328 * Below works because anonymous area would not have a > 1329 * transparent huge PUD. If file-backed support is added, > 1330 * that case would need to be handled here. > 1331 */ > 1332 src_pmd = mm_find_pmd(src_mm, src_addr); > 1333 if (unlikely(!src_pmd)) { > 1334 if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { > 1335 err = -ENOENT; > 1336 break; > 1337 } > 1338 src_pmd = mm_alloc_pmd(src_mm, src_addr); > 1339 if (unlikely(!src_pmd)) { > 1340 err = -ENOMEM; > 1341 break; > 1342 } > 1343 } > 1344 dst_pmd = mm_alloc_pmd(dst_mm, dst_addr); > 1345 if (unlikely(!dst_pmd)) { > 1346 err = -ENOMEM; > 1347 break; > 1348 } > 1349 > 1350 dst_pmdval = pmdp_get_lockless(dst_pmd); > 1351 /* > 1352 * If the dst_pmd is mapped as THP don't override it and just > 1353 * be strict. If dst_pmd changes into TPH after this check, the > 1354 * remap_pages_huge_pmd() will detect the change and retry > 1355 * while remap_pages_pte() will detect the change and fail. > 1356 */ > 1357 if (unlikely(pmd_trans_huge(dst_pmdval))) { > 1358 err = -EEXIST; > 1359 break; > 1360 } > 1361 > 1362 ptl = pmd_trans_huge_lock(src_pmd, src_vma); > 1363 if (ptl) { > 1364 if (pmd_devmap(*src_pmd)) { > 1365 spin_unlock(ptl); > 1366 err = -ENOENT; > 1367 break; > 1368 } > 1369 > 1370 /* > 1371 * Check if we can move the pmd without > 1372 * splitting it. First check the address > 1373 * alignment to be the same in src/dst. These > 1374 * checks don't actually need the PT lock but > 1375 * it's good to do it here to optimize this > 1376 * block away at build time if > 1377 * CONFIG_TRANSPARENT_HUGEPAGE is not set. > 1378 */ > 1379 if ((src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) || > > 1380 src_start + len - src_addr < HPAGE_PMD_SIZE || !pmd_none(dst_pmdval)) { > > -- > 0-DAY CI Kernel Test Service > https://github.com/intel/lkp-tests/wiki > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx. >
