// SPDX-License-Identifier: GPL-2.0-only /* * mm/userfaultfd.c * * Copyright (C) 2015 Red Hat, Inc. */ #include #include #include #include #include #include #include #include #include #include #include #include #include "internal.h" static __always_inline bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end) { /* Make sure that the dst range is fully within dst_vma. */ if (dst_end > dst_vma->vm_end) return false; /* * Check the vma is registered in uffd, this is required to * enforce the VM_MAYWRITE check done at uffd registration * time. */ if (!dst_vma->vm_userfaultfd_ctx.ctx) return false; return true; } static __always_inline struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm, unsigned long addr) { struct vm_area_struct *vma; mmap_assert_locked(mm); vma = vma_lookup(mm, addr); if (!vma) vma = ERR_PTR(-ENOENT); else if (!(vma->vm_flags & VM_SHARED) && unlikely(anon_vma_prepare(vma))) vma = ERR_PTR(-ENOMEM); return vma; } #ifdef CONFIG_PER_VMA_LOCK /* * lock_vma() - Lookup and lock vma corresponding to @address. * @mm: mm to search vma in. * @address: address that the vma should contain. * * Should be called without holding mmap_lock. vma should be unlocked after use * with unlock_vma(). * * Return: A locked vma containing @address, -ENOENT if no vma is found, or * -ENOMEM if anon_vma couldn't be allocated. */ static struct vm_area_struct *lock_vma(struct mm_struct *mm, unsigned long address) { struct vm_area_struct *vma; vma = lock_vma_under_rcu(mm, address); if (vma) { /* * lock_vma_under_rcu() only checks anon_vma for private * anonymous mappings. But we need to ensure it is assigned in * private file-backed vmas as well. */ if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma)) vma_end_read(vma); else return vma; } mmap_read_lock(mm); vma = find_vma_and_prepare_anon(mm, address); if (!IS_ERR(vma)) { /* * We cannot use vma_start_read() as it may fail due to * false locked (see comment in vma_start_read()). We * can avoid that by directly locking vm_lock under * mmap_lock, which guarantees that nobody can lock the * vma for write (vma_start_write()) under us. */ down_read(&vma->vm_lock->lock); } mmap_read_unlock(mm); return vma; } static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm, unsigned long dst_start, unsigned long len) { struct vm_area_struct *dst_vma; dst_vma = lock_vma(dst_mm, dst_start); if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len)) return dst_vma; vma_end_read(dst_vma); return ERR_PTR(-ENOENT); } static void uffd_mfill_unlock(struct vm_area_struct *vma) { vma_end_read(vma); } #else static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm, unsigned long dst_start, unsigned long len) { struct vm_area_struct *dst_vma; mmap_read_lock(dst_mm); dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start); if (IS_ERR(dst_vma)) goto out_unlock; if (validate_dst_vma(dst_vma, dst_start + len)) return dst_vma; dst_vma = ERR_PTR(-ENOENT); out_unlock: mmap_read_unlock(dst_mm); return dst_vma; } static void uffd_mfill_unlock(struct vm_area_struct *vma) { mmap_read_unlock(vma->vm_mm); } #endif /* Check if dst_addr is outside of file's size. Must be called with ptl held. */ static bool mfill_file_over_size(struct vm_area_struct *dst_vma, unsigned long dst_addr) { struct inode *inode; pgoff_t offset, max_off; if (!dst_vma->vm_file) return false; inode = dst_vma->vm_file->f_inode; offset = linear_page_index(dst_vma, dst_addr); max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); return offset >= max_off; } /* * Install PTEs, to map dst_addr (within dst_vma) to page. * * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem * and anon, and for both shared and private VMAs. */ int mfill_atomic_install_pte(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, struct page *page, bool newly_allocated, uffd_flags_t flags) { int ret; struct mm_struct *dst_mm = dst_vma->vm_mm; pte_t _dst_pte, *dst_pte; bool writable = dst_vma->vm_flags & VM_WRITE; bool vm_shared = dst_vma->vm_flags & VM_SHARED; bool page_in_cache = page_mapping(page); spinlock_t *ptl; struct folio *folio; _dst_pte = mk_pte(page, dst_vma->vm_page_prot); _dst_pte = pte_mkdirty(_dst_pte); if (page_in_cache && !vm_shared) writable = false; if (writable) _dst_pte = pte_mkwrite(_dst_pte, dst_vma); if (flags & MFILL_ATOMIC_WP) _dst_pte = pte_mkuffd_wp(_dst_pte); ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); if (!dst_pte) goto out; if (mfill_file_over_size(dst_vma, dst_addr)) { ret = -EFAULT; goto out_unlock; } ret = -EEXIST; /* * We allow to overwrite a pte marker: consider when both MISSING|WP * registered, we firstly wr-protect a none pte which has no page cache * page backing it, then access the page. */ if (!pte_none_mostly(ptep_get(dst_pte))) goto out_unlock; folio = page_folio(page); if (page_in_cache) { /* Usually, cache pages are already added to LRU */ if (newly_allocated) folio_add_lru(folio); folio_add_file_rmap_pte(folio, page, dst_vma); } else { folio_add_new_anon_rmap(folio, dst_vma, dst_addr); folio_add_lru_vma(folio, dst_vma); } /* * Must happen after rmap, as mm_counter() checks mapping (via * PageAnon()), which is set by __page_set_anon_rmap(). */ inc_mm_counter(dst_mm, mm_counter(folio)); set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); /* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret = 0; out_unlock: pte_unmap_unlock(dst_pte, ptl); out: return ret; } static int mfill_atomic_pte_copy(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, unsigned long src_addr, uffd_flags_t flags, struct folio **foliop) { void *kaddr; int ret; struct folio *folio; if (!*foliop) { ret = -ENOMEM; folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma, dst_addr, false); if (!folio) goto out; kaddr = kmap_local_folio(folio, 0); /* * The read mmap_lock is held here. Despite the * mmap_lock being read recursive a deadlock is still * possible if a writer has taken a lock. For example: * * process A thread 1 takes read lock on own mmap_lock * process A thread 2 calls mmap, blocks taking write lock * process B thread 1 takes page fault, read lock on own mmap lock * process B thread 2 calls mmap, blocks taking write lock * process A thread 1 blocks taking read lock on process B * process B thread 1 blocks taking read lock on process A * * Disable page faults to prevent potential deadlock * and retry the copy outside the mmap_lock. */ pagefault_disable(); ret = copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE); pagefault_enable(); kunmap_local(kaddr); /* fallback to copy_from_user outside mmap_lock */ if (unlikely(ret)) { ret = -ENOENT; *foliop = folio; /* don't free the page */ goto out; } flush_dcache_folio(folio); } else { folio = *foliop; *foliop = NULL; } /* * The memory barrier inside __folio_mark_uptodate makes sure that * preceding stores to the page contents become visible before * the set_pte_at() write. */ __folio_mark_uptodate(folio); ret = -ENOMEM; if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL)) goto out_release; ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, &folio->page, true, flags); if (ret) goto out_release; out: return ret; out_release: folio_put(folio); goto out; } static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr) { pte_t _dst_pte, *dst_pte; spinlock_t *ptl; int ret; _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr), dst_vma->vm_page_prot)); ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl); if (!dst_pte) goto out; if (mfill_file_over_size(dst_vma, dst_addr)) { ret = -EFAULT; goto out_unlock; } ret = -EEXIST; if (!pte_none(ptep_get(dst_pte))) goto out_unlock; set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte); /* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret = 0; out_unlock: pte_unmap_unlock(dst_pte, ptl); out: return ret; } /* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */ static int mfill_atomic_pte_continue(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, uffd_flags_t flags) { struct inode *inode = file_inode(dst_vma->vm_file); pgoff_t pgoff = linear_page_index(dst_vma, dst_addr); struct folio *folio; struct page *page; int ret; ret = shmem_get_folio(inode, pgoff, &folio, SGP_NOALLOC); /* Our caller expects us to return -EFAULT if we failed to find folio */ if (ret == -ENOENT) ret = -EFAULT; if (ret) goto out; if (!folio) { ret = -EFAULT; goto out; } page = folio_file_page(folio, pgoff); if (PageHWPoison(page)) { ret = -EIO; goto out_release; } ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, page, false, flags); if (ret) goto out_release; folio_unlock(folio); ret = 0; out: return ret; out_release: folio_unlock(folio); folio_put(folio); goto out; } /* Handles UFFDIO_POISON for all non-hugetlb VMAs. */ static int mfill_atomic_pte_poison(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, uffd_flags_t flags) { int ret; struct mm_struct *dst_mm = dst_vma->vm_mm; pte_t _dst_pte, *dst_pte; spinlock_t *ptl; _dst_pte = make_pte_marker(PTE_MARKER_POISONED); ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); if (!dst_pte) goto out; if (mfill_file_over_size(dst_vma, dst_addr)) { ret = -EFAULT; goto out_unlock; } ret = -EEXIST; /* Refuse to overwrite any PTE, even a PTE marker (e.g. UFFD WP). */ if (!pte_none(ptep_get(dst_pte))) goto out_unlock; set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); /* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret = 0; out_unlock: pte_unmap_unlock(dst_pte, ptl); out: return ret; } static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address) { pgd_t *pgd; p4d_t *p4d; pud_t *pud; pgd = pgd_offset(mm, address); p4d = p4d_alloc(mm, pgd, address); if (!p4d) return NULL; pud = pud_alloc(mm, p4d, address); if (!pud) return NULL; /* * Note that we didn't run this because the pmd was * missing, the *pmd may be already established and in * turn it may also be a trans_huge_pmd. */ return pmd_alloc(mm, pud, address); } #ifdef CONFIG_HUGETLB_PAGE /* * mfill_atomic processing for HUGETLB vmas. Note that this routine is * called with either vma-lock or mmap_lock held, it will release the lock * before returning. */ static __always_inline ssize_t mfill_atomic_hugetlb( struct userfaultfd_ctx *ctx, struct vm_area_struct *dst_vma, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags) { struct mm_struct *dst_mm = dst_vma->vm_mm; ssize_t err; pte_t *dst_pte; unsigned long src_addr, dst_addr; long copied; struct folio *folio; unsigned long vma_hpagesize; pgoff_t idx; u32 hash; struct address_space *mapping; /* * There is no default zero huge page for all huge page sizes as * supported by hugetlb. A PMD_SIZE huge pages may exist as used * by THP. Since we can not reliably insert a zero page, this * feature is not supported. */ if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) { up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); return -EINVAL; } src_addr = src_start; dst_addr = dst_start; copied = 0; folio = NULL; vma_hpagesize = vma_kernel_pagesize(dst_vma); /* * Validate alignment based on huge page size */ err = -EINVAL; if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1)) goto out_unlock; retry: /* * On routine entry dst_vma is set. If we had to drop mmap_lock and * retry, dst_vma will be set to NULL and we must lookup again. */ if (!dst_vma) { dst_vma = uffd_mfill_lock(dst_mm, dst_start, len); if (IS_ERR(dst_vma)) { err = PTR_ERR(dst_vma); goto out; } err = -ENOENT; if (!is_vm_hugetlb_page(dst_vma)) goto out_unlock_vma; err = -EINVAL; if (vma_hpagesize != vma_kernel_pagesize(dst_vma)) goto out_unlock_vma; /* * If memory mappings are changing because of non-cooperative * operation (e.g. mremap) running in parallel, bail out and * request the user to retry later */ down_read(&ctx->map_changing_lock); err = -EAGAIN; if (atomic_read(&ctx->mmap_changing)) goto out_unlock; } while (src_addr < src_start + len) { BUG_ON(dst_addr >= dst_start + len); /* * Serialize via vma_lock and hugetlb_fault_mutex. * vma_lock ensures the dst_pte remains valid even * in the case of shared pmds. fault mutex prevents * races with other faulting threads. */ idx = linear_page_index(dst_vma, dst_addr); mapping = dst_vma->vm_file->f_mapping; hash = hugetlb_fault_mutex_hash(mapping, idx); mutex_lock(&hugetlb_fault_mutex_table[hash]); hugetlb_vma_lock_read(dst_vma); err = -ENOMEM; dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize); if (!dst_pte) { hugetlb_vma_unlock_read(dst_vma); mutex_unlock(&hugetlb_fault_mutex_table[hash]); goto out_unlock; } if (!uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) && !huge_pte_none_mostly(huge_ptep_get(dst_pte))) { err = -EEXIST; hugetlb_vma_unlock_read(dst_vma); mutex_unlock(&hugetlb_fault_mutex_table[hash]); goto out_unlock; } err = hugetlb_mfill_atomic_pte(dst_pte, dst_vma, dst_addr, src_addr, flags, &folio); hugetlb_vma_unlock_read(dst_vma); mutex_unlock(&hugetlb_fault_mutex_table[hash]); cond_resched(); if (unlikely(err == -ENOENT)) { up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); BUG_ON(!folio); err = copy_folio_from_user(folio, (const void __user *)src_addr, true); if (unlikely(err)) { err = -EFAULT; goto out; } dst_vma = NULL; goto retry; } else BUG_ON(folio); if (!err) { dst_addr += vma_hpagesize; src_addr += vma_hpagesize; copied += vma_hpagesize; if (fatal_signal_pending(current)) err = -EINTR; } if (err) break; } out_unlock: up_read(&ctx->map_changing_lock); out_unlock_vma: uffd_mfill_unlock(dst_vma); out: if (folio) folio_put(folio); BUG_ON(copied < 0); BUG_ON(err > 0); BUG_ON(!copied && !err); return copied ? copied : err; } #else /* !CONFIG_HUGETLB_PAGE */ /* fail at build time if gcc attempts to use this */ extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx, struct vm_area_struct *dst_vma, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags); #endif /* CONFIG_HUGETLB_PAGE */ static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, unsigned long src_addr, uffd_flags_t flags, struct folio **foliop) { ssize_t err; if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) { return mfill_atomic_pte_continue(dst_pmd, dst_vma, dst_addr, flags); } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) { return mfill_atomic_pte_poison(dst_pmd, dst_vma, dst_addr, flags); } /* * The normal page fault path for a shmem will invoke the * fault, fill the hole in the file and COW it right away. The * result generates plain anonymous memory. So when we are * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll * generate anonymous memory directly without actually filling * the hole. For the MAP_PRIVATE case the robustness check * only happens in the pagetable (to verify it's still none) * and not in the radix tree. */ if (!(dst_vma->vm_flags & VM_SHARED)) { if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) err = mfill_atomic_pte_copy(dst_pmd, dst_vma, dst_addr, src_addr, flags, foliop); else err = mfill_atomic_pte_zeropage(dst_pmd, dst_vma, dst_addr); } else { err = shmem_mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, src_addr, flags, foliop); } return err; } static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags) { struct mm_struct *dst_mm = ctx->mm; struct vm_area_struct *dst_vma; ssize_t err; pmd_t *dst_pmd; unsigned long src_addr, dst_addr; long copied; struct folio *folio; /* * Sanitize the command parameters: */ BUG_ON(dst_start & ~PAGE_MASK); BUG_ON(len & ~PAGE_MASK); /* Does the address range wrap, or is the span zero-sized? */ BUG_ON(src_start + len <= src_start); BUG_ON(dst_start + len <= dst_start); src_addr = src_start; dst_addr = dst_start; copied = 0; folio = NULL; retry: /* * Make sure the vma is not shared, that the dst range is * both valid and fully within a single existing vma. */ dst_vma = uffd_mfill_lock(dst_mm, dst_start, len); if (IS_ERR(dst_vma)) { err = PTR_ERR(dst_vma); goto out; } /* * If memory mappings are changing because of non-cooperative * operation (e.g. mremap) running in parallel, bail out and * request the user to retry later */ down_read(&ctx->map_changing_lock); err = -EAGAIN; if (atomic_read(&ctx->mmap_changing)) goto out_unlock; err = -EINVAL; /* * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but * it will overwrite vm_ops, so vma_is_anonymous must return false. */ if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) && dst_vma->vm_flags & VM_SHARED)) goto out_unlock; /* * validate 'mode' now that we know the dst_vma: don't allow * a wrprotect copy if the userfaultfd didn't register as WP. */ if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) goto out_unlock; /* * If this is a HUGETLB vma, pass off to appropriate routine */ if (is_vm_hugetlb_page(dst_vma)) return mfill_atomic_hugetlb(ctx, dst_vma, dst_start, src_start, len, flags); if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) goto out_unlock; if (!vma_is_shmem(dst_vma) && uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) goto out_unlock; while (src_addr < src_start + len) { pmd_t dst_pmdval; BUG_ON(dst_addr >= dst_start + len); dst_pmd = mm_alloc_pmd(dst_mm, dst_addr); if (unlikely(!dst_pmd)) { err = -ENOMEM; break; } dst_pmdval = pmdp_get_lockless(dst_pmd); /* * If the dst_pmd is mapped as THP don't * override it and just be strict. */ if (unlikely(pmd_trans_huge(dst_pmdval))) { err = -EEXIST; break; } if (unlikely(pmd_none(dst_pmdval)) && unlikely(__pte_alloc(dst_mm, dst_pmd))) { err = -ENOMEM; break; } /* If an huge pmd materialized from under us fail */ if (unlikely(pmd_trans_huge(*dst_pmd))) { err = -EFAULT; break; } BUG_ON(pmd_none(*dst_pmd)); BUG_ON(pmd_trans_huge(*dst_pmd)); err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, src_addr, flags, &folio); cond_resched(); if (unlikely(err == -ENOENT)) { void *kaddr; up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); BUG_ON(!folio); kaddr = kmap_local_folio(folio, 0); err = copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE); kunmap_local(kaddr); if (unlikely(err)) { err = -EFAULT; goto out; } flush_dcache_folio(folio); goto retry; } else BUG_ON(folio); if (!err) { dst_addr += PAGE_SIZE; src_addr += PAGE_SIZE; copied += PAGE_SIZE; if (fatal_signal_pending(current)) err = -EINTR; } if (err) break; } out_unlock: up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); out: if (folio) folio_put(folio); BUG_ON(copied < 0); BUG_ON(err > 0); BUG_ON(!copied && !err); return copied ? copied : err; } ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags) { return mfill_atomic(ctx, dst_start, src_start, len, uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY)); } ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len) { return mfill_atomic(ctx, start, 0, len, uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE)); } ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, uffd_flags_t flags) { /* * A caller might reasonably assume that UFFDIO_CONTINUE contains an * smp_wmb() to ensure that any writes to the about-to-be-mapped page by * the thread doing the UFFDIO_CONTINUE are guaranteed to be visible to * subsequent loads from the page through the newly mapped address range. */ smp_wmb(); return mfill_atomic(ctx, start, 0, len, uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE)); } ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, uffd_flags_t flags) { return mfill_atomic(ctx, start, 0, len, uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON)); } long uffd_wp_range(struct vm_area_struct *dst_vma, unsigned long start, unsigned long len, bool enable_wp) { unsigned int mm_cp_flags; struct mmu_gather tlb; long ret; VM_WARN_ONCE(start < dst_vma->vm_start || start + len > dst_vma->vm_end, "The address range exceeds VMA boundary.\n"); if (enable_wp) mm_cp_flags = MM_CP_UFFD_WP; else mm_cp_flags = MM_CP_UFFD_WP_RESOLVE; /* * vma->vm_page_prot already reflects that uffd-wp is enabled for this * VMA (see userfaultfd_set_vm_flags()) and that all PTEs are supposed * to be write-protected as default whenever protection changes. * Try upgrading write permissions manually. */ if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma)) mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE; tlb_gather_mmu(&tlb, dst_vma->vm_mm); ret = change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags); tlb_finish_mmu(&tlb); return ret; } int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, bool enable_wp) { struct mm_struct *dst_mm = ctx->mm; unsigned long end = start + len; unsigned long _start, _end; struct vm_area_struct *dst_vma; unsigned long page_mask; long err; VMA_ITERATOR(vmi, dst_mm, start); /* * Sanitize the command parameters: */ BUG_ON(start & ~PAGE_MASK); BUG_ON(len & ~PAGE_MASK); /* Does the address range wrap, or is the span zero-sized? */ BUG_ON(start + len <= start); mmap_read_lock(dst_mm); /* * If memory mappings are changing because of non-cooperative * operation (e.g. mremap) running in parallel, bail out and * request the user to retry later */ down_read(&ctx->map_changing_lock); err = -EAGAIN; if (atomic_read(&ctx->mmap_changing)) goto out_unlock; err = -ENOENT; for_each_vma_range(vmi, dst_vma, end) { if (!userfaultfd_wp(dst_vma)) { err = -ENOENT; break; } if (is_vm_hugetlb_page(dst_vma)) { err = -EINVAL; page_mask = vma_kernel_pagesize(dst_vma) - 1; if ((start & page_mask) || (len & page_mask)) break; } _start = max(dst_vma->vm_start, start); _end = min(dst_vma->vm_end, end); err = uffd_wp_range(dst_vma, _start, _end - _start, enable_wp); /* Return 0 on success, <0 on failures */ if (err < 0) break; err = 0; } out_unlock: up_read(&ctx->map_changing_lock); mmap_read_unlock(dst_mm); return err; } void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2) __acquires(ptl1) __acquires(ptl2) { spinlock_t *ptl_tmp; if (ptl1 > ptl2) { /* exchange ptl1 and ptl2 */ ptl_tmp = ptl1; ptl1 = ptl2; ptl2 = ptl_tmp; } /* lock in virtual address order to avoid lock inversion */ spin_lock(ptl1); if (ptl1 != ptl2) spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING); else __acquire(ptl2); } void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2) __releases(ptl1) __releases(ptl2) { spin_unlock(ptl1); if (ptl1 != ptl2) spin_unlock(ptl2); else __release(ptl2); } static int move_present_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, spinlock_t *dst_ptl, spinlock_t *src_ptl, struct folio *src_folio) { int err = 0; double_pt_lock(dst_ptl, src_ptl); if (!pte_same(ptep_get(src_pte), orig_src_pte) || !pte_same(ptep_get(dst_pte), orig_dst_pte)) { err = -EAGAIN; goto out; } if (folio_test_large(src_folio) || folio_maybe_dma_pinned(src_folio) || !PageAnonExclusive(&src_folio->page)) { err = -EBUSY; goto out; } orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte); /* Folio got pinned from under us. Put it back and fail the move. */ if (folio_maybe_dma_pinned(src_folio)) { set_pte_at(mm, src_addr, src_pte, orig_src_pte); err = -EBUSY; goto out; } folio_move_anon_rmap(src_folio, dst_vma); WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr)); orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot); /* Follow mremap() behavior and treat the entry dirty after the move */ orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma); set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte); out: double_pt_unlock(dst_ptl, src_ptl); return err; } static int move_swap_pte(struct mm_struct *mm, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, spinlock_t *dst_ptl, spinlock_t *src_ptl) { if (!pte_swp_exclusive(orig_src_pte)) return -EBUSY; double_pt_lock(dst_ptl, src_ptl); if (!pte_same(ptep_get(src_pte), orig_src_pte) || !pte_same(ptep_get(dst_pte), orig_dst_pte)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; } orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); double_pt_unlock(dst_ptl, src_ptl); return 0; } static int move_zeropage_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, spinlock_t *dst_ptl, spinlock_t *src_ptl) { pte_t zero_pte; double_pt_lock(dst_ptl, src_ptl); if (!pte_same(ptep_get(src_pte), orig_src_pte) || !pte_same(ptep_get(dst_pte), orig_dst_pte)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; } zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr), dst_vma->vm_page_prot)); ptep_clear_flush(src_vma, src_addr, src_pte); set_pte_at(mm, dst_addr, dst_pte, zero_pte); double_pt_unlock(dst_ptl, src_ptl); return 0; } /* * The mmap_lock for reading is held by the caller. Just move the page * from src_pmd to dst_pmd if possible, and return true if succeeded * in moving the page. */ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long dst_addr, unsigned long src_addr, __u64 mode) { swp_entry_t entry; pte_t orig_src_pte, orig_dst_pte; pte_t src_folio_pte; spinlock_t *src_ptl, *dst_ptl; pte_t *src_pte = NULL; pte_t *dst_pte = NULL; struct folio *src_folio = NULL; struct anon_vma *src_anon_vma = NULL; struct mmu_notifier_range range; int err = 0; flush_cache_range(src_vma, src_addr, src_addr + PAGE_SIZE); mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, src_addr, src_addr + PAGE_SIZE); mmu_notifier_invalidate_range_start(&range); retry: dst_pte = pte_offset_map_nolock(mm, dst_pmd, dst_addr, &dst_ptl); /* Retry if a huge pmd materialized from under us */ if (unlikely(!dst_pte)) { err = -EAGAIN; goto out; } src_pte = pte_offset_map_nolock(mm, src_pmd, src_addr, &src_ptl); /* * We held the mmap_lock for reading so MADV_DONTNEED * can zap transparent huge pages under us, or the * transparent huge page fault can establish new * transparent huge pages under us. */ if (unlikely(!src_pte)) { err = -EAGAIN; goto out; } /* Sanity checks before the operation */ if (WARN_ON_ONCE(pmd_none(*dst_pmd)) || WARN_ON_ONCE(pmd_none(*src_pmd)) || WARN_ON_ONCE(pmd_trans_huge(*dst_pmd)) || WARN_ON_ONCE(pmd_trans_huge(*src_pmd))) { err = -EINVAL; goto out; } spin_lock(dst_ptl); orig_dst_pte = ptep_get(dst_pte); spin_unlock(dst_ptl); if (!pte_none(orig_dst_pte)) { err = -EEXIST; goto out; } spin_lock(src_ptl); orig_src_pte = ptep_get(src_pte); spin_unlock(src_ptl); if (pte_none(orig_src_pte)) { if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) err = -ENOENT; else /* nothing to do to move a hole */ err = 0; goto out; } /* If PTE changed after we locked the folio them start over */ if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) { err = -EAGAIN; goto out; } if (pte_present(orig_src_pte)) { if (is_zero_pfn(pte_pfn(orig_src_pte))) { err = move_zeropage_pte(mm, dst_vma, src_vma, dst_addr, src_addr, dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_ptl, src_ptl); goto out; } /* * Pin and lock both source folio and anon_vma. Since we are in * RCU read section, we can't block, so on contention have to * unmap the ptes, obtain the lock and retry. */ if (!src_folio) { struct folio *folio; /* * Pin the page while holding the lock to be sure the * page isn't freed under us */ spin_lock(src_ptl); if (!pte_same(orig_src_pte, ptep_get(src_pte))) { spin_unlock(src_ptl); err = -EAGAIN; goto out; } folio = vm_normal_folio(src_vma, src_addr, orig_src_pte); if (!folio || !PageAnonExclusive(&folio->page)) { spin_unlock(src_ptl); err = -EBUSY; goto out; } folio_get(folio); src_folio = folio; src_folio_pte = orig_src_pte; spin_unlock(src_ptl); if (!folio_trylock(src_folio)) { pte_unmap(&orig_src_pte); pte_unmap(&orig_dst_pte); src_pte = dst_pte = NULL; /* now we can block and wait */ folio_lock(src_folio); goto retry; } if (WARN_ON_ONCE(!folio_test_anon(src_folio))) { err = -EBUSY; goto out; } } /* at this point we have src_folio locked */ if (folio_test_large(src_folio)) { /* split_folio() can block */ pte_unmap(&orig_src_pte); pte_unmap(&orig_dst_pte); src_pte = dst_pte = NULL; err = split_folio(src_folio); if (err) goto out; /* have to reacquire the folio after it got split */ folio_unlock(src_folio); folio_put(src_folio); src_folio = NULL; goto retry; } if (!src_anon_vma) { /* * folio_referenced walks the anon_vma chain * without the folio lock. Serialize against it with * the anon_vma lock, the folio lock is not enough. */ src_anon_vma = folio_get_anon_vma(src_folio); if (!src_anon_vma) { /* page was unmapped from under us */ err = -EAGAIN; goto out; } if (!anon_vma_trylock_write(src_anon_vma)) { pte_unmap(&orig_src_pte); pte_unmap(&orig_dst_pte); src_pte = dst_pte = NULL; /* now we can block and wait */ anon_vma_lock_write(src_anon_vma); goto retry; } } err = move_present_pte(mm, dst_vma, src_vma, dst_addr, src_addr, dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_ptl, src_ptl, src_folio); } else { entry = pte_to_swp_entry(orig_src_pte); if (non_swap_entry(entry)) { if (is_migration_entry(entry)) { pte_unmap(&orig_src_pte); pte_unmap(&orig_dst_pte); src_pte = dst_pte = NULL; migration_entry_wait(mm, src_pmd, src_addr); err = -EAGAIN; } else err = -EFAULT; goto out; } err = move_swap_pte(mm, dst_addr, src_addr, dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_ptl, src_ptl); } out: if (src_anon_vma) { anon_vma_unlock_write(src_anon_vma); put_anon_vma(src_anon_vma); } if (src_folio) { folio_unlock(src_folio); folio_put(src_folio); } if (dst_pte) pte_unmap(dst_pte); if (src_pte) pte_unmap(src_pte); mmu_notifier_invalidate_range_end(&range); return err; } #ifdef CONFIG_TRANSPARENT_HUGEPAGE static inline bool move_splits_huge_pmd(unsigned long dst_addr, unsigned long src_addr, unsigned long src_end) { return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) || src_end - src_addr < HPAGE_PMD_SIZE; } #else static inline bool move_splits_huge_pmd(unsigned long dst_addr, unsigned long src_addr, unsigned long src_end) { /* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */ return false; } #endif static inline bool vma_move_compatible(struct vm_area_struct *vma) { return !(vma->vm_flags & (VM_PFNMAP | VM_IO | VM_HUGETLB | VM_MIXEDMAP | VM_SHADOW_STACK)); } static int validate_move_areas(struct userfaultfd_ctx *ctx, struct vm_area_struct *src_vma, struct vm_area_struct *dst_vma) { /* Only allow moving if both have the same access and protection */ if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) || pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot)) return -EINVAL; /* Only allow moving if both are mlocked or both aren't */ if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED)) return -EINVAL; /* * For now, we keep it simple and only move between writable VMAs. * Access flags are equal, therefore cheching only the source is enough. */ if (!(src_vma->vm_flags & VM_WRITE)) return -EINVAL; /* Check if vma flags indicate content which can be moved */ if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma)) return -EINVAL; /* Ensure dst_vma is registered in uffd we are operating on */ if (!dst_vma->vm_userfaultfd_ctx.ctx || dst_vma->vm_userfaultfd_ctx.ctx != ctx) return -EINVAL; /* Only allow moving across anonymous vmas */ if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma)) return -EINVAL; return 0; } static __always_inline int find_vmas_mm_locked(struct mm_struct *mm, unsigned long dst_start, unsigned long src_start, struct vm_area_struct **dst_vmap, struct vm_area_struct **src_vmap) { struct vm_area_struct *vma; mmap_assert_locked(mm); vma = find_vma_and_prepare_anon(mm, dst_start); if (IS_ERR(vma)) return PTR_ERR(vma); *dst_vmap = vma; /* Skip finding src_vma if src_start is in dst_vma */ if (src_start >= vma->vm_start && src_start < vma->vm_end) goto out_success; vma = vma_lookup(mm, src_start); if (!vma) return -ENOENT; out_success: *src_vmap = vma; return 0; } #ifdef CONFIG_PER_VMA_LOCK static int uffd_move_lock(struct mm_struct *mm, unsigned long dst_start, unsigned long src_start, struct vm_area_struct **dst_vmap, struct vm_area_struct **src_vmap) { struct vm_area_struct *vma; int err; vma = lock_vma(mm, dst_start); if (IS_ERR(vma)) return PTR_ERR(vma); *dst_vmap = vma; /* * Skip finding src_vma if src_start is in dst_vma. This also ensures * that we don't lock the same vma twice. */ if (src_start >= vma->vm_start && src_start < vma->vm_end) { *src_vmap = vma; return 0; } /* * Using lock_vma() to get src_vma can lead to following deadlock: * * Thread1 Thread2 * ------- ------- * vma_start_read(dst_vma) * mmap_write_lock(mm) * vma_start_write(src_vma) * vma_start_read(src_vma) * mmap_read_lock(mm) * vma_start_write(dst_vma) */ *src_vmap = lock_vma_under_rcu(mm, src_start); if (likely(*src_vmap)) return 0; /* Undo any locking and retry in mmap_lock critical section */ vma_end_read(*dst_vmap); mmap_read_lock(mm); err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (!err) { /* * See comment in lock_vma() as to why not using * vma_start_read() here. */ down_read(&(*dst_vmap)->vm_lock->lock); if (*dst_vmap != *src_vmap) down_read_nested(&(*src_vmap)->vm_lock->lock, SINGLE_DEPTH_NESTING); } mmap_read_unlock(mm); return err; } static void uffd_move_unlock(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) { vma_end_read(src_vma); if (src_vma != dst_vma) vma_end_read(dst_vma); } #else static int uffd_move_lock(struct mm_struct *mm, unsigned long dst_start, unsigned long src_start, struct vm_area_struct **dst_vmap, struct vm_area_struct **src_vmap) { int err; mmap_read_lock(mm); err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (err) mmap_read_unlock(mm); return err; } static void uffd_move_unlock(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) { mmap_assert_locked(src_vma->vm_mm); mmap_read_unlock(dst_vma->vm_mm); } #endif /** * move_pages - move arbitrary anonymous pages of an existing vma * @ctx: pointer to the userfaultfd context * @dst_start: start of the destination virtual memory range * @src_start: start of the source virtual memory range * @len: length of the virtual memory range * @mode: flags from uffdio_move.mode * * It will either use the mmap_lock in read mode or per-vma locks * * move_pages() remaps arbitrary anonymous pages atomically in zero * copy. It only works on non shared anonymous pages because those can * be relocated without generating non linear anon_vmas in the rmap * code. * * It provides a zero copy mechanism to handle userspace page faults. * The source vma pages should have mapcount == 1, which can be * enforced by using madvise(MADV_DONTFORK) on src vma. * * The thread receiving the page during the userland page fault * will receive the faulting page in the source vma through the network, * storage or any other I/O device (MADV_DONTFORK in the source vma * avoids move_pages() to fail with -EBUSY if the process forks before * move_pages() is called), then it will call move_pages() to map the * page in the faulting address in the destination vma. * * This userfaultfd command works purely via pagetables, so it's the * most efficient way to move physical non shared anonymous pages * across different virtual addresses. Unlike mremap()/mmap()/munmap() * it does not create any new vmas. The mapping in the destination * address is atomic. * * It only works if the vma protection bits are identical from the * source and destination vma. * * It can remap non shared anonymous pages within the same vma too. * * If the source virtual memory range has any unmapped holes, or if * the destination virtual memory range is not a whole unmapped hole, * move_pages() will fail respectively with -ENOENT or -EEXIST. This * provides a very strict behavior to avoid any chance of memory * corruption going unnoticed if there are userland race conditions. * Only one thread should resolve the userland page fault at any given * time for any given faulting address. This means that if two threads * try to both call move_pages() on the same destination address at the * same time, the second thread will get an explicit error from this * command. * * The command retval will return "len" is successful. The command * however can be interrupted by fatal signals or errors. If * interrupted it will return the number of bytes successfully * remapped before the interruption if any, or the negative error if * none. It will never return zero. Either it will return an error or * an amount of bytes successfully moved. If the retval reports a * "short" remap, the move_pages() command should be repeated by * userland with src+retval, dst+reval, len-retval if it wants to know * about the error that interrupted it. * * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to * prevent -ENOENT errors to materialize if there are holes in the * source virtual range that is being remapped. The holes will be * accounted as successfully remapped in the retval of the * command. This is mostly useful to remap hugepage naturally aligned * virtual regions without knowing if there are transparent hugepage * in the regions or not, but preventing the risk of having to split * the hugepmd during the remap. * * If there's any rmap walk that is taking the anon_vma locks without * first obtaining the folio lock (the only current instance is * folio_referenced), they will have to verify if the folio->mapping * has changed after taking the anon_vma lock. If it changed they * should release the lock and retry obtaining a new anon_vma, because * it means the anon_vma was changed by move_pages() before the lock * could be obtained. This is the only additional complexity added to * the rmap code to provide this anonymous page remapping functionality. */ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, __u64 mode) { struct mm_struct *mm = ctx->mm; struct vm_area_struct *src_vma, *dst_vma; unsigned long src_addr, dst_addr; pmd_t *src_pmd, *dst_pmd; long err = -EINVAL; ssize_t moved = 0; /* Sanitize the command parameters. */ if (WARN_ON_ONCE(src_start & ~PAGE_MASK) || WARN_ON_ONCE(dst_start & ~PAGE_MASK) || WARN_ON_ONCE(len & ~PAGE_MASK)) goto out; /* Does the address range wrap, or is the span zero-sized? */ if (WARN_ON_ONCE(src_start + len <= src_start) || WARN_ON_ONCE(dst_start + len <= dst_start)) goto out; err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma); if (err) goto out; /* Re-check after taking map_changing_lock */ err = -EAGAIN; down_read(&ctx->map_changing_lock); if (likely(atomic_read(&ctx->mmap_changing))) goto out_unlock; /* * Make sure the vma is not shared, that the src and dst remap * ranges are both valid and fully within a single existing * vma. */ err = -EINVAL; if (src_vma->vm_flags & VM_SHARED) goto out_unlock; if (src_start + len > src_vma->vm_end) goto out_unlock; if (dst_vma->vm_flags & VM_SHARED) goto out_unlock; if (dst_start + len > dst_vma->vm_end) goto out_unlock; err = validate_move_areas(ctx, src_vma, dst_vma); if (err) goto out_unlock; for (src_addr = src_start, dst_addr = dst_start; src_addr < src_start + len;) { spinlock_t *ptl; pmd_t dst_pmdval; unsigned long step_size; /* * Below works because anonymous area would not have a * transparent huge PUD. If file-backed support is added, * that case would need to be handled here. */ src_pmd = mm_find_pmd(mm, src_addr); if (unlikely(!src_pmd)) { if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { err = -ENOENT; break; } src_pmd = mm_alloc_pmd(mm, src_addr); if (unlikely(!src_pmd)) { err = -ENOMEM; break; } } dst_pmd = mm_alloc_pmd(mm, dst_addr); if (unlikely(!dst_pmd)) { err = -ENOMEM; break; } dst_pmdval = pmdp_get_lockless(dst_pmd); /* * If the dst_pmd is mapped as THP don't override it and just * be strict. If dst_pmd changes into TPH after this check, the * move_pages_huge_pmd() will detect the change and retry * while move_pages_pte() will detect the change and fail. */ if (unlikely(pmd_trans_huge(dst_pmdval))) { err = -EEXIST; break; } ptl = pmd_trans_huge_lock(src_pmd, src_vma); if (ptl) { if (pmd_devmap(*src_pmd)) { spin_unlock(ptl); err = -ENOENT; break; } /* Check if we can move the pmd without splitting it. */ if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || !pmd_none(dst_pmdval)) { struct folio *folio = pfn_folio(pmd_pfn(*src_pmd)); if (!folio || (!is_huge_zero_page(&folio->page) && !PageAnonExclusive(&folio->page))) { spin_unlock(ptl); err = -EBUSY; break; } spin_unlock(ptl); split_huge_pmd(src_vma, src_pmd, src_addr); /* The folio will be split by move_pages_pte() */ continue; } err = move_pages_huge_pmd(mm, dst_pmd, src_pmd, dst_pmdval, dst_vma, src_vma, dst_addr, src_addr); step_size = HPAGE_PMD_SIZE; } else { if (pmd_none(*src_pmd)) { if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { err = -ENOENT; break; } if (unlikely(__pte_alloc(mm, src_pmd))) { err = -ENOMEM; break; } } if (unlikely(pte_alloc(mm, dst_pmd))) { err = -ENOMEM; break; } err = move_pages_pte(mm, dst_pmd, src_pmd, dst_vma, src_vma, dst_addr, src_addr, mode); step_size = PAGE_SIZE; } cond_resched(); if (fatal_signal_pending(current)) { /* Do not override an error */ if (!err || err == -EAGAIN) err = -EINTR; break; } if (err) { if (err == -EAGAIN) continue; break; } /* Proceed to the next page */ dst_addr += step_size; src_addr += step_size; moved += step_size; } out_unlock: up_read(&ctx->map_changing_lock); uffd_move_unlock(dst_vma, src_vma); out: VM_WARN_ON(moved < 0); VM_WARN_ON(err > 0); VM_WARN_ON(!moved && !err); return moved ? moved : err; }