/* * linux/mm/mlock.c * * (C) Copyright 1995 Linus Torvalds * (C) Copyright 2002 Christoph Hellwig */ #include <linux/capability.h> #include <linux/mman.h> #include <linux/mm.h> #include <linux/swap.h> #include <linux/swapops.h> #include <linux/pagemap.h> #include <linux/mempolicy.h> #include <linux/syscalls.h> #include <linux/sched.h> #include <linux/module.h> #include <linux/rmap.h> #include <linux/mmzone.h> #include <linux/hugetlb.h> #include "internal.h" int can_do_mlock(void) { if (capable(CAP_IPC_LOCK)) return 1; if (rlimit(RLIMIT_MEMLOCK) != 0) return 1; return 0; } EXPORT_SYMBOL(can_do_mlock); /* * Mlocked pages are marked with PageMlocked() flag for efficient testing * in vmscan and, possibly, the fault path; and to support semi-accurate * statistics. * * An mlocked page [PageMlocked(page)] is unevictable. As such, it will * be placed on the LRU "unevictable" list, rather than the [in]active lists. * The unevictable list is an LRU sibling list to the [in]active lists. * PageUnevictable is set to indicate the unevictable state. * * When lazy mlocking via vmscan, it is important to ensure that the * vma's VM_LOCKED status is not concurrently being modified, otherwise we * may have mlocked a page that is being munlocked. So lazy mlock must take * the mmap_sem for read, and verify that the vma really is locked * (see mm/rmap.c). */ /* * LRU accounting for clear_page_mlock() */ void __clear_page_mlock(struct page *page) { VM_BUG_ON(!PageLocked(page)); if (!page->mapping) { /* truncated ? */ return; } dec_zone_page_state(page, NR_MLOCK); count_vm_event(UNEVICTABLE_PGCLEARED); if (!isolate_lru_page(page)) { putback_lru_page(page); } else { /* * We lost the race. the page already moved to evictable list. */ if (PageUnevictable(page)) count_vm_event(UNEVICTABLE_PGSTRANDED); } } /* * Mark page as mlocked if not already. * If page on LRU, isolate and putback to move to unevictable list. */ void mlock_vma_page(struct page *page) { BUG_ON(!PageLocked(page)); if (!TestSetPageMlocked(page)) { inc_zone_page_state(page, NR_MLOCK); count_vm_event(UNEVICTABLE_PGMLOCKED); if (!isolate_lru_page(page)) putback_lru_page(page); } } /** * munlock_vma_page - munlock a vma page * @page - page to be unlocked * * called from munlock()/munmap() path with page supposedly on the LRU. * When we munlock a page, because the vma where we found the page is being * munlock()ed or munmap()ed, we want to check whether other vmas hold the * page locked so that we can leave it on the unevictable lru list and not * bother vmscan with it. However, to walk the page's rmap list in * try_to_munlock() we must isolate the page from the LRU. If some other * task has removed the page from the LRU, we won't be able to do that. * So we clear the PageMlocked as we might not get another chance. If we * can't isolate the page, we leave it for putback_lru_page() and vmscan * [page_referenced()/try_to_unmap()] to deal with. */ void munlock_vma_page(struct page *page) { BUG_ON(!PageLocked(page)); if (TestClearPageMlocked(page)) { dec_zone_page_state(page, NR_MLOCK); if (!isolate_lru_page(page)) { int ret = try_to_munlock(page); /* * did try_to_unlock() succeed or punt? */ if (ret != SWAP_MLOCK) count_vm_event(UNEVICTABLE_PGMUNLOCKED); putback_lru_page(page); } else { /* * Some other task has removed the page from the LRU. * putback_lru_page() will take care of removing the * page from the unevictable list, if necessary. * vmscan [page_referenced()] will move the page back * to the unevictable list if some other vma has it * mlocked. */ if (PageUnevictable(page)) count_vm_event(UNEVICTABLE_PGSTRANDED); else count_vm_event(UNEVICTABLE_PGMUNLOCKED); } } } /** * __mlock_vma_pages_range() - mlock a range of pages in the vma. * @vma: target vma * @start: start address * @end: end address * * This takes care of making the pages present too. * * return 0 on success, negative error code on error. * * vma->vm_mm->mmap_sem must be held for at least read. */ static long __mlock_vma_pages_range(struct vm_area_struct *vma, unsigned long start, unsigned long end) { struct mm_struct *mm = vma->vm_mm; unsigned long addr = start; struct page *pages[16]; /* 16 gives a reasonable batch */ int nr_pages = (end - start) / PAGE_SIZE; int ret = 0; int gup_flags; VM_BUG_ON(start & ~PAGE_MASK); VM_BUG_ON(end & ~PAGE_MASK); VM_BUG_ON(start < vma->vm_start); VM_BUG_ON(end > vma->vm_end); VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); gup_flags = FOLL_TOUCH | FOLL_GET; if (vma->vm_flags & VM_WRITE) gup_flags |= FOLL_WRITE; while (nr_pages > 0) { int i; cond_resched(); /* * get_user_pages makes pages present if we are * setting mlock. and this extra reference count will * disable migration of this page. However, page may * still be truncated out from under us. */ ret = __get_user_pages(current, mm, addr, min_t(int, nr_pages, ARRAY_SIZE(pages)), gup_flags, pages, NULL); /* * This can happen for, e.g., VM_NONLINEAR regions before * a page has been allocated and mapped at a given offset, * or for addresses that map beyond end of a file. * We'll mlock the pages if/when they get faulted in. */ if (ret < 0) break; lru_add_drain(); /* push cached pages to LRU */ for (i = 0; i < ret; i++) { struct page *page = pages[i]; if (page->mapping) { /* * That preliminary check is mainly to avoid * the pointless overhead of lock_page on the * ZERO_PAGE: which might bounce very badly if * there is contention. However, we're still * dirtying its cacheline with get/put_page: * we'll add another __get_user_pages flag to * avoid it if that case turns out to matter. */ lock_page(page); /* * Because we lock page here and migration is * blocked by the elevated reference, we need * only check for file-cache page truncation. */ if (page->mapping) mlock_vma_page(page); unlock_page(page); } put_page(page); /* ref from get_user_pages() */ } addr += ret * PAGE_SIZE; nr_pages -= ret; ret = 0; } return ret; /* 0 or negative error code */ } /* * convert get_user_pages() return value to posix mlock() error */ static int __mlock_posix_error_return(long retval) { if (retval == -EFAULT) retval = -ENOMEM; else if (retval == -ENOMEM) retval = -EAGAIN; return retval; } /** * mlock_vma_pages_range() - mlock pages in specified vma range. * @vma - the vma containing the specfied address range * @start - starting address in @vma to mlock * @end - end address [+1] in @vma to mlock * * For mmap()/mremap()/expansion of mlocked vma. * * return 0 on success for "normal" vmas. * * return number of pages [> 0] to be removed from locked_vm on success * of "special" vmas. */ long mlock_vma_pages_range(struct vm_area_struct *vma, unsigned long start, unsigned long end) { int nr_pages = (end - start) / PAGE_SIZE; BUG_ON(!(vma->vm_flags & VM_LOCKED)); /* * filter unlockable vmas */ if (vma->vm_flags & (VM_IO | VM_PFNMAP)) goto no_mlock; if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) || is_vm_hugetlb_page(vma) || vma == get_gate_vma(current))) { __mlock_vma_pages_range(vma, start, end); /* Hide errors from mmap() and other callers */ return 0; } /* * User mapped kernel pages or huge pages: * make these pages present to populate the ptes, but * fall thru' to reset VM_LOCKED--no need to unlock, and * return nr_pages so these don't get counted against task's * locked limit. huge pages are already counted against * locked vm limit. */ make_pages_present(start, end); no_mlock: vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */ return nr_pages; /* error or pages NOT mlocked */ } /* * munlock_vma_pages_range() - munlock all pages in the vma range.' * @vma - vma containing range to be munlock()ed. * @start - start address in @vma of the range * @end - end of range in @vma. * * For mremap(), munmap() and exit(). * * Called with @vma VM_LOCKED. * * Returns with VM_LOCKED cleared. Callers must be prepared to * deal with this. * * We don't save and restore VM_LOCKED here because pages are * still on lru. In unmap path, pages might be scanned by reclaim * and re-mlocked by try_to_{munlock|unmap} before we unmap and * free them. This will result in freeing mlocked pages. */ void munlock_vma_pages_range(struct vm_area_struct *vma, unsigned long start, unsigned long end) { unsigned long addr; lru_add_drain(); vma->vm_flags &= ~VM_LOCKED; for (addr = start; addr < end; addr += PAGE_SIZE) { struct page *page; /* * Although FOLL_DUMP is intended for get_dump_page(), * it just so happens that its special treatment of the * ZERO_PAGE (returning an error instead of doing get_page) * suits munlock very well (and if somehow an abnormal page * has sneaked into the range, we won't oops here: great). */ page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); if (page && !IS_ERR(page)) { lock_page(page); /* * Like in __mlock_vma_pages_range(), * because we lock page here and migration is * blocked by the elevated reference, we need * only check for file-cache page truncation. */ if (page->mapping) munlock_vma_page(page); unlock_page(page); put_page(page); } cond_resched(); } } /* * mlock_fixup - handle mlock[all]/munlock[all] requests. * * Filters out "special" vmas -- VM_LOCKED never gets set for these, and * munlock is a no-op. However, for some special vmas, we go ahead and * populate the ptes via make_pages_present(). * * For vmas that pass the filters, merge/split as appropriate. */ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev, unsigned long start, unsigned long end, unsigned int newflags) { struct mm_struct *mm = vma->vm_mm; pgoff_t pgoff; int nr_pages; int ret = 0; int lock = newflags & VM_LOCKED; if (newflags == vma->vm_flags || (vma->vm_flags & (VM_IO | VM_PFNMAP))) goto out; /* don't set VM_LOCKED, don't count */ if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) || is_vm_hugetlb_page(vma) || vma == get_gate_vma(current)) { if (lock) make_pages_present(start, end); goto out; /* don't set VM_LOCKED, don't count */ } pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma)); if (*prev) { vma = *prev; goto success; } if (start != vma->vm_start) { ret = split_vma(mm, vma, start, 1); if (ret) goto out; } if (end != vma->vm_end) { ret = split_vma(mm, vma, end, 0); if (ret) goto out; } success: /* * Keep track of amount of locked VM. */ nr_pages = (end - start) >> PAGE_SHIFT; if (!lock) nr_pages = -nr_pages; mm->locked_vm += nr_pages; /* * vm_flags is protected by the mmap_sem held in write mode. * It's okay if try_to_unmap_one unmaps a page just after we * set VM_LOCKED, __mlock_vma_pages_range will bring it back. */ if (lock) { vma->vm_flags = newflags; ret = __mlock_vma_pages_range(vma, start, end); if (ret < 0) ret = __mlock_posix_error_return(ret); } else { munlock_vma_pages_range(vma, start, end); } out: *prev = vma; return ret; } static int do_mlock(unsigned long start, size_t len, int on) { unsigned long nstart, end, tmp; struct vm_area_struct * vma, * prev; int error; len = PAGE_ALIGN(len); end = start + len; if (end < start) return -EINVAL; if (end == start) return 0; vma = find_vma_prev(current->mm, start, &prev); if (!vma || vma->vm_start > start) return -ENOMEM; if (start > vma->vm_start) prev = vma; for (nstart = start ; ; ) { unsigned int newflags; /* Here we know that vma->vm_start <= nstart < vma->vm_end. */ newflags = vma->vm_flags | VM_LOCKED; if (!on) newflags &= ~VM_LOCKED; tmp = vma->vm_end; if (tmp > end) tmp = end; error = mlock_fixup(vma, &prev, nstart, tmp, newflags); if (error) break; nstart = tmp; if (nstart < prev->vm_end) nstart = prev->vm_end; if (nstart >= end) break; vma = prev->vm_next; if (!vma || vma->vm_start != nstart) { error = -ENOMEM; break; } } return error; } SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len) { unsigned long locked; unsigned long lock_limit; int error = -ENOMEM; if (!can_do_mlock()) return -EPERM; lru_add_drain_all(); /* flush pagevec */ down_write(¤t->mm->mmap_sem); len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); start &= PAGE_MASK; locked = len >> PAGE_SHIFT; locked += current->mm->locked_vm; lock_limit = rlimit(RLIMIT_MEMLOCK); lock_limit >>= PAGE_SHIFT; /* check against resource limits */ if ((locked <= lock_limit) || capable(CAP_IPC_LOCK)) error = do_mlock(start, len, 1); up_write(¤t->mm->mmap_sem); return error; } SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) { int ret; down_write(¤t->mm->mmap_sem); len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); start &= PAGE_MASK; ret = do_mlock(start, len, 0); up_write(¤t->mm->mmap_sem); return ret; } static int do_mlockall(int flags) { struct vm_area_struct * vma, * prev = NULL; unsigned int def_flags = 0; if (flags & MCL_FUTURE) def_flags = VM_LOCKED; current->mm->def_flags = def_flags; if (flags == MCL_FUTURE) goto out; for (vma = current->mm->mmap; vma ; vma = prev->vm_next) { unsigned int newflags; newflags = vma->vm_flags | VM_LOCKED; if (!(flags & MCL_CURRENT)) newflags &= ~VM_LOCKED; /* Ignore errors */ mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); } out: return 0; } SYSCALL_DEFINE1(mlockall, int, flags) { unsigned long lock_limit; int ret = -EINVAL; if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE))) goto out; ret = -EPERM; if (!can_do_mlock()) goto out; lru_add_drain_all(); /* flush pagevec */ down_write(¤t->mm->mmap_sem); lock_limit = rlimit(RLIMIT_MEMLOCK); lock_limit >>= PAGE_SHIFT; ret = -ENOMEM; if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) || capable(CAP_IPC_LOCK)) ret = do_mlockall(flags); up_write(¤t->mm->mmap_sem); out: return ret; } SYSCALL_DEFINE0(munlockall) { int ret; down_write(¤t->mm->mmap_sem); ret = do_mlockall(0); up_write(¤t->mm->mmap_sem); return ret; } /* * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB * shm segments) get accounted against the user_struct instead. */ static DEFINE_SPINLOCK(shmlock_user_lock); int user_shm_lock(size_t size, struct user_struct *user) { unsigned long lock_limit, locked; int allowed = 0; locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; lock_limit = rlimit(RLIMIT_MEMLOCK); if (lock_limit == RLIM_INFINITY) allowed = 1; lock_limit >>= PAGE_SHIFT; spin_lock(&shmlock_user_lock); if (!allowed && locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK)) goto out; get_uid(user); user->locked_shm += locked; allowed = 1; out: spin_unlock(&shmlock_user_lock); return allowed; } void user_shm_unlock(size_t size, struct user_struct *user) { spin_lock(&shmlock_user_lock); user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT; spin_unlock(&shmlock_user_lock); free_uid(user); }