Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 793 insertions, 0 deletions

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
new file mode 100644
index 000000000..650ab6cfd
--- /dev/null
+++ b/mm/userfaultfd.c
@@ -0,0 +1,793 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  mm/userfaultfd.c
+ *
+ *  Copyright (C) 2015  Red Hat, Inc.
+ */
+
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/userfaultfd_k.h>
+#include <linux/mmu_notifier.h>
+#include <linux/hugetlb.h>
+#include <linux/shmem_fs.h>
+#include <asm/tlbflush.h>
+#include <asm/tlb.h>
+#include "internal.h"
+
+static __always_inline
+struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
+				    unsigned long dst_start,
+				    unsigned long len)
+{
+	/*
+	 * Make sure that the dst range is both valid and fully within a
+	 * single existing vma.
+	 */
+	struct vm_area_struct *dst_vma;
+
+	dst_vma = find_vma(dst_mm, dst_start);
+	if (!dst_vma)
+		return NULL;
+
+	if (dst_start < dst_vma->vm_start ||
+	    dst_start + len > dst_vma->vm_end)
+		return NULL;
+
+	/*
+	 * 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 NULL;
+
+	return dst_vma;
+}
+
+/*
+ * 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(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+			     struct vm_area_struct *dst_vma,
+			     unsigned long dst_addr, struct page *page,
+			     bool newly_allocated, bool wp_copy)
+{
+	int ret;
+	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 inode *inode;
+	pgoff_t offset, max_off;
+
+	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
+	_dst_pte = pte_mkdirty(_dst_pte);
+	if (page_in_cache && !vm_shared)
+		writable = false;
+
+	/*
+	 * Always mark a PTE as write-protected when needed, regardless of
+	 * VM_WRITE, which the user might change.
+	 */
+	if (wp_copy) {
+		_dst_pte = pte_mkuffd_wp(_dst_pte);
+		writable = false;
+	}
+
+	if (writable)
+		_dst_pte = pte_mkwrite(_dst_pte);
+	else
+		/*
+		 * We need this to make sure write bit removed; as mk_pte()
+		 * could return a pte with write bit set.
+		 */
+		_dst_pte = pte_wrprotect(_dst_pte);
+
+	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+
+	if (vma_is_shmem(dst_vma)) {
+		/* serialize against truncate with the page table lock */
+		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);
+		ret = -EFAULT;
+		if (unlikely(offset >= max_off))
+			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(*dst_pte))
+		goto out_unlock;
+
+	if (page_in_cache) {
+		/* Usually, cache pages are already added to LRU */
+		if (newly_allocated)
+			lru_cache_add(page);
+		page_add_file_rmap(page, dst_vma, false);
+	} else {
+		page_add_new_anon_rmap(page, dst_vma, dst_addr);
+		lru_cache_add_inactive_or_unevictable(page, 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(page));
+
+	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);
+	return ret;
+}
+
+static int mcopy_atomic_pte(struct mm_struct *dst_mm,
+			    pmd_t *dst_pmd,
+			    struct vm_area_struct *dst_vma,
+			    unsigned long dst_addr,
+			    unsigned long src_addr,
+			    struct page **pagep,
+			    bool wp_copy)
+{
+	void *page_kaddr;
+	int ret;
+	struct page *page;
+
+	if (!*pagep) {
+		ret = -ENOMEM;
+		page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
+		if (!page)
+			goto out;
+
+		page_kaddr = kmap_local_page(page);
+		/*
+		 * 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(page_kaddr,
+				     (const void __user *) src_addr,
+				     PAGE_SIZE);
+		pagefault_enable();
+		kunmap_local(page_kaddr);
+
+		/* fallback to copy_from_user outside mmap_lock */
+		if (unlikely(ret)) {
+			ret = -ENOENT;
+			*pagep = page;
+			/* don't free the page */
+			goto out;
+		}
+
+		flush_dcache_page(page);
+	} else {
+		page = *pagep;
+		*pagep = NULL;
+	}
+
+	/*
+	 * The memory barrier inside __SetPageUptodate makes sure that
+	 * preceding stores to the page contents become visible before
+	 * the set_pte_at() write.
+	 */
+	__SetPageUptodate(page);
+
+	ret = -ENOMEM;
+	if (mem_cgroup_charge(page_folio(page), dst_mm, GFP_KERNEL))
+		goto out_release;
+
+	ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
+				       page, true, wp_copy);
+	if (ret)
+		goto out_release;
+out:
+	return ret;
+out_release:
+	put_page(page);
+	goto out;
+}
+
+static int mfill_zeropage_pte(struct mm_struct *dst_mm,
+			      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;
+	pgoff_t offset, max_off;
+	struct inode *inode;
+
+	_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
+					 dst_vma->vm_page_prot));
+	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+	if (dst_vma->vm_file) {
+		/* the shmem MAP_PRIVATE case requires checking the i_size */
+		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);
+		ret = -EFAULT;
+		if (unlikely(offset >= max_off))
+			goto out_unlock;
+	}
+	ret = -EEXIST;
+	if (!pte_none(*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);
+	return ret;
+}
+
+/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
+static int mcontinue_atomic_pte(struct mm_struct *dst_mm,
+				pmd_t *dst_pmd,
+				struct vm_area_struct *dst_vma,
+				unsigned long dst_addr,
+				bool wp_copy)
+{
+	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_mm, dst_pmd, dst_vma, dst_addr,
+				       page, false, wp_copy);
+	if (ret)
+		goto out_release;
+
+	folio_unlock(folio);
+	ret = 0;
+out:
+	return ret;
+out_release:
+	folio_unlock(folio);
+	folio_put(folio);
+	goto out;
+}
+
+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
+/*
+ * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
+ * called with mmap_lock held, it will release mmap_lock before returning.
+ */
+static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
+					      struct vm_area_struct *dst_vma,
+					      unsigned long dst_start,
+					      unsigned long src_start,
+					      unsigned long len,
+					      enum mcopy_atomic_mode mode,
+					      bool wp_copy)
+{
+	int vm_shared = dst_vma->vm_flags & VM_SHARED;
+	ssize_t err;
+	pte_t *dst_pte;
+	unsigned long src_addr, dst_addr;
+	long copied;
+	struct page *page;
+	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 (mode == MCOPY_ATOMIC_ZEROPAGE) {
+		mmap_read_unlock(dst_mm);
+		return -EINVAL;
+	}
+
+	src_addr = src_start;
+	dst_addr = dst_start;
+	copied = 0;
+	page = 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) {
+		err = -ENOENT;
+		dst_vma = find_dst_vma(dst_mm, dst_start, len);
+		if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
+			goto out_unlock;
+
+		err = -EINVAL;
+		if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
+			goto out_unlock;
+
+		vm_shared = dst_vma->vm_flags & VM_SHARED;
+	}
+
+	/*
+	 * If not shared, ensure the dst_vma has a anon_vma.
+	 */
+	err = -ENOMEM;
+	if (!vm_shared) {
+		if (unlikely(anon_vma_prepare(dst_vma)))
+			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 (mode != MCOPY_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_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
+					       dst_addr, src_addr, mode, &page,
+					       wp_copy);
+
+		hugetlb_vma_unlock_read(dst_vma);
+		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+
+		cond_resched();
+
+		if (unlikely(err == -ENOENT)) {
+			mmap_read_unlock(dst_mm);
+			BUG_ON(!page);
+
+			err = copy_huge_page_from_user(page,
+						(const void __user *)src_addr,
+						vma_hpagesize / PAGE_SIZE,
+						true);
+			if (unlikely(err)) {
+				err = -EFAULT;
+				goto out;
+			}
+			mmap_read_lock(dst_mm);
+
+			dst_vma = NULL;
+			goto retry;
+		} else
+			BUG_ON(page);
+
+		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:
+	mmap_read_unlock(dst_mm);
+out:
+	if (page)
+		put_page(page);
+	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 __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
+				      struct vm_area_struct *dst_vma,
+				      unsigned long dst_start,
+				      unsigned long src_start,
+				      unsigned long len,
+				      enum mcopy_atomic_mode mode,
+				      bool wp_copy);
+#endif /* CONFIG_HUGETLB_PAGE */
+
+static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
+						pmd_t *dst_pmd,
+						struct vm_area_struct *dst_vma,
+						unsigned long dst_addr,
+						unsigned long src_addr,
+						struct page **page,
+						enum mcopy_atomic_mode mode,
+						bool wp_copy)
+{
+	ssize_t err;
+
+	if (mode == MCOPY_ATOMIC_CONTINUE) {
+		return mcontinue_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
+					    wp_copy);
+	}
+
+	/*
+	 * 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 (mode == MCOPY_ATOMIC_NORMAL)
+			err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
+					       dst_addr, src_addr, page,
+					       wp_copy);
+		else
+			err = mfill_zeropage_pte(dst_mm, dst_pmd,
+						 dst_vma, dst_addr);
+	} else {
+		err = shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
+					     dst_addr, src_addr,
+					     mode != MCOPY_ATOMIC_NORMAL,
+					     wp_copy, page);
+	}
+
+	return err;
+}
+
+static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
+					      unsigned long dst_start,
+					      unsigned long src_start,
+					      unsigned long len,
+					      enum mcopy_atomic_mode mcopy_mode,
+					      atomic_t *mmap_changing,
+					      __u64 mode)
+{
+	struct vm_area_struct *dst_vma;
+	ssize_t err;
+	pmd_t *dst_pmd;
+	unsigned long src_addr, dst_addr;
+	long copied;
+	struct page *page;
+	bool wp_copy;
+
+	/*
+	 * 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;
+	page = NULL;
+retry:
+	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
+	 */
+	err = -EAGAIN;
+	if (mmap_changing && atomic_read(mmap_changing))
+		goto out_unlock;
+
+	/*
+	 * Make sure the vma is not shared, that the dst range is
+	 * both valid and fully within a single existing vma.
+	 */
+	err = -ENOENT;
+	dst_vma = find_dst_vma(dst_mm, dst_start, len);
+	if (!dst_vma)
+		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.
+	 */
+	wp_copy = mode & UFFDIO_COPY_MODE_WP;
+	if (wp_copy && !(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  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
+					       src_start, len, mcopy_mode,
+					       wp_copy);
+
+	if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
+		goto out_unlock;
+	if (!vma_is_shmem(dst_vma) && mcopy_mode == MCOPY_ATOMIC_CONTINUE)
+		goto out_unlock;
+
+	/*
+	 * Ensure the dst_vma has a anon_vma or this page
+	 * would get a NULL anon_vma when moved in the
+	 * dst_vma.
+	 */
+	err = -ENOMEM;
+	if (!(dst_vma->vm_flags & VM_SHARED) &&
+	    unlikely(anon_vma_prepare(dst_vma)))
+		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 = pmd_read_atomic(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_mm, dst_pmd, dst_vma, dst_addr,
+				       src_addr, &page, mcopy_mode, wp_copy);
+		cond_resched();
+
+		if (unlikely(err == -ENOENT)) {
+			void *page_kaddr;
+
+			mmap_read_unlock(dst_mm);
+			BUG_ON(!page);
+
+			page_kaddr = kmap_local_page(page);
+			err = copy_from_user(page_kaddr,
+					     (const void __user *) src_addr,
+					     PAGE_SIZE);
+			kunmap_local(page_kaddr);
+			if (unlikely(err)) {
+				err = -EFAULT;
+				goto out;
+			}
+			flush_dcache_page(page);
+			goto retry;
+		} else
+			BUG_ON(page);
+
+		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:
+	mmap_read_unlock(dst_mm);
+out:
+	if (page)
+		put_page(page);
+	BUG_ON(copied < 0);
+	BUG_ON(err > 0);
+	BUG_ON(!copied && !err);
+	return copied ? copied : err;
+}
+
+ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
+		     unsigned long src_start, unsigned long len,
+		     atomic_t *mmap_changing, __u64 mode)
+{
+	return __mcopy_atomic(dst_mm, dst_start, src_start, len,
+			      MCOPY_ATOMIC_NORMAL, mmap_changing, mode);
+}
+
+ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
+		       unsigned long len, atomic_t *mmap_changing)
+{
+	return __mcopy_atomic(dst_mm, start, 0, len, MCOPY_ATOMIC_ZEROPAGE,
+			      mmap_changing, 0);
+}
+
+ssize_t mcopy_continue(struct mm_struct *dst_mm, unsigned long start,
+		       unsigned long len, atomic_t *mmap_changing)
+{
+	return __mcopy_atomic(dst_mm, start, 0, len, MCOPY_ATOMIC_CONTINUE,
+			      mmap_changing, 0);
+}
+
+void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma,
+		   unsigned long start, unsigned long len, bool enable_wp)
+{
+	struct mmu_gather tlb;
+	pgprot_t newprot;
+
+	if (enable_wp)
+		newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
+	else
+		newprot = vm_get_page_prot(dst_vma->vm_flags);
+
+	tlb_gather_mmu(&tlb, dst_mm);
+	change_protection(&tlb, dst_vma, start, start + len, newprot,
+			  enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE);
+	tlb_finish_mmu(&tlb);
+}
+
+int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
+			unsigned long len, bool enable_wp,
+			atomic_t *mmap_changing)
+{
+	struct vm_area_struct *dst_vma;
+	unsigned long page_mask;
+	int err;
+
+	/*
+	 * 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
+	 */
+	err = -EAGAIN;
+	if (mmap_changing && atomic_read(mmap_changing))
+		goto out_unlock;
+
+	err = -ENOENT;
+	dst_vma = find_dst_vma(dst_mm, start, len);
+
+	if (!dst_vma)
+		goto out_unlock;
+	if (!userfaultfd_wp(dst_vma))
+		goto out_unlock;
+	if (!vma_can_userfault(dst_vma, dst_vma->vm_flags))
+		goto out_unlock;
+
+	if (is_vm_hugetlb_page(dst_vma)) {
+		err = -EINVAL;
+		page_mask = vma_kernel_pagesize(dst_vma) - 1;
+		if ((start & page_mask) || (len & page_mask))
+			goto out_unlock;
+	}
+
+	uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp);
+
+	err = 0;
+out_unlock:
+	mmap_read_unlock(dst_mm);
+	return err;
+}