mm/userfaultfd.c - linux - Git at Google

 // 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 "internal.h"

 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)
 {
 	struct mem_cgroup *memcg;
 	pte_t _dst_pte, *dst_pte;
 	spinlock_t *ptl;
 	void *page_kaddr;
 	int ret;
 	struct page *page;
 	pgoff_t offset, max_off;
 	struct inode *inode;

 	if (!*pagep) {
 		ret = -ENOMEM;
 		page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
 		if (!page)
 			goto out;

 		page_kaddr = kmap_atomic(page);
 		ret = copy_from_user(page_kaddr,
 				     (const void __user *) src_addr,
 				     PAGE_SIZE);
 		kunmap_atomic(page_kaddr);

 		/* fallback to copy_from_user outside mmap_sem */
 		if (unlikely(ret)) {
 			ret = -ENOENT;
 			*pagep = page;
 			/* don't free the page */
 			goto out;
 		}
 	} else {
 		page = *pagep;
 		*pagep = NULL;
 	}

 	/*
 	 * The memory barrier inside __SetPageUptodate makes sure that
 	 * preceeding stores to the page contents become visible before
 	 * the set_pte_at() write.
 	 */
 	__SetPageUptodate(page);

 	ret = -ENOMEM;
 	if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
 		goto out_release;

 	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
 	if (dst_vma->vm_flags & VM_WRITE)
 		_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));

 	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_release_uncharge_unlock;
 	}
 	ret = -EEXIST;
 	if (!pte_none(*dst_pte))
 		goto out_release_uncharge_unlock;

 	inc_mm_counter(dst_mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
 	mem_cgroup_commit_charge(page, memcg, false, false);
 	lru_cache_add_active_or_unevictable(page, dst_vma);

 	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);

 	pte_unmap_unlock(dst_pte, ptl);
 	ret = 0;
 out:
 	return ret;
 out_release_uncharge_unlock:
 	pte_unmap_unlock(dst_pte, ptl);
 	mem_cgroup_cancel_charge(page, memcg, false);
 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;
 }

 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_sem held, it will release mmap_sem 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,
 					      bool zeropage)
 {
 	int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
 	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;
 	struct hstate *h;
 	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 (zeropage) {
 		up_read(&dst_mm->mmap_sem);
 		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_sem and
 	 * retry, dst_vma will be set to NULL and we must lookup again.
 	 */
 	if (!dst_vma) {
 		err = -ENOENT;
 		dst_vma = find_vma(dst_mm, dst_start);
 		if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
 			goto out_unlock;
 		/*
 		 * 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)
 			goto out_unlock;

 		if (dst_start < dst_vma->vm_start ||
 		    dst_start + len > dst_vma->vm_end)
 			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 (WARN_ON(dst_addr & (vma_hpagesize - 1) ||
 		    (len - copied) & (vma_hpagesize - 1)))
 		goto out_unlock;

 	/*
 	 * 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;
 	}

 	h = hstate_vma(dst_vma);

 	while (src_addr < src_start + len) {
 		pte_t dst_pteval;

 		BUG_ON(dst_addr >= dst_start + len);
 		VM_BUG_ON(dst_addr & ~huge_page_mask(h));

 		/*
 		 * Serialize via hugetlb_fault_mutex
 		 */
 		idx = linear_page_index(dst_vma, dst_addr);
 		mapping = dst_vma->vm_file->f_mapping;
 		hash = hugetlb_fault_mutex_hash(h, mapping, idx, dst_addr);
 		mutex_lock(&hugetlb_fault_mutex_table[hash]);

 		err = -ENOMEM;
 		dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h));
 		if (!dst_pte) {
 			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 			goto out_unlock;
 		}

 		err = -EEXIST;
 		dst_pteval = huge_ptep_get(dst_pte);
 		if (!huge_pte_none(dst_pteval)) {
 			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, &page);

 		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 		vm_alloc_shared = vm_shared;

 		cond_resched();

 		if (unlikely(err == -ENOENT)) {
 			up_read(&dst_mm->mmap_sem);
 			BUG_ON(!page);

 			err = copy_huge_page_from_user(page,
 						(const void __user *)src_addr,
 						pages_per_huge_page(h), true);
 			if (unlikely(err)) {
 				err = -EFAULT;
 				goto out;
 			}
 			down_read(&dst_mm->mmap_sem);

 			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:
 	up_read(&dst_mm->mmap_sem);
 out:
 	if (page) {
 		/*
 		 * We encountered an error and are about to free a newly
 		 * allocated huge page.
 		 *
 		 * Reservation handling is very subtle, and is different for
 		 * private and shared mappings.  See the routine
 		 * restore_reserve_on_error for details.  Unfortunately, we
 		 * can not call restore_reserve_on_error now as it would
 		 * require holding mmap_sem.
 		 *
 		 * If a reservation for the page existed in the reservation
 		 * map of a private mapping, the map was modified to indicate
 		 * the reservation was consumed when the page was allocated.
 		 * We clear the PagePrivate flag now so that the global
 		 * reserve count will not be incremented in free_huge_page.
 		 * The reservation map will still indicate the reservation
 		 * was consumed and possibly prevent later page allocation.
 		 * This is better than leaking a global reservation.  If no
 		 * reservation existed, it is still safe to clear PagePrivate
 		 * as no adjustments to reservation counts were made during
 		 * allocation.
 		 *
 		 * The reservation map for shared mappings indicates which
 		 * pages have reservations.  When a huge page is allocated
 		 * for an address with a reservation, no change is made to
 		 * the reserve map.  In this case PagePrivate will be set
 		 * to indicate that the global reservation count should be
 		 * incremented when the page is freed.  This is the desired
 		 * behavior.  However, when a huge page is allocated for an
 		 * address without a reservation a reservation entry is added
 		 * to the reservation map, and PagePrivate will not be set.
 		 * When the page is freed, the global reserve count will NOT
 		 * be incremented and it will appear as though we have leaked
 		 * reserved page.  In this case, set PagePrivate so that the
 		 * global reserve count will be incremented to match the
 		 * reservation map entry which was created.
 		 *
 		 * Note that vm_alloc_shared is based on the flags of the vma
 		 * for which the page was originally allocated.  dst_vma could
 		 * be different or NULL on error.
 		 */
 		if (vm_alloc_shared)
 			SetPagePrivate(page);
 		else
 			ClearPagePrivate(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,
 				      bool zeropage);
 #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,
 						bool zeropage)
 {
 	ssize_t err;

 	/*
 	 * 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 (!zeropage)
 			err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
 					       dst_addr, src_addr, page);
 		else
 			err = mfill_zeropage_pte(dst_mm, dst_pmd,
 						 dst_vma, dst_addr);
 	} else {
 		if (!zeropage)
 			err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
 						     dst_vma, dst_addr,
 						     src_addr, page);
 		else
 			err = shmem_mfill_zeropage_pte(dst_mm, dst_pmd,
 						       dst_vma, dst_addr);
 	}

 	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,
 					      bool zeropage,
 					      bool *mmap_changing)
 {
 	struct vm_area_struct *dst_vma;
 	ssize_t err;
 	pmd_t *dst_pmd;
 	unsigned long src_addr, dst_addr;
 	long copied;
 	struct page *page;

 	/*
 	 * 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:
 	down_read(&dst_mm->mmap_sem);

 	/*
 	 * 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 && READ_ONCE(*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_vma(dst_mm, dst_start);
 	if (!dst_vma)
 		goto out_unlock;
 	/*
 	 * 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)
 		goto out_unlock;

 	if (dst_start < dst_vma->vm_start ||
 	    dst_start + len > dst_vma->vm_end)
 		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;

 	/*
 	 * 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, zeropage);

 	if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
 		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, zeropage);
 		cond_resched();

 		if (unlikely(err == -ENOENT)) {
 			void *page_kaddr;

 			up_read(&dst_mm->mmap_sem);
 			BUG_ON(!page);

 			page_kaddr = kmap(page);
 			err = copy_from_user(page_kaddr,
 					     (const void __user *) src_addr,
 					     PAGE_SIZE);
 			kunmap(page);
 			if (unlikely(err)) {
 				err = -EFAULT;
 				goto out;
 			}
 			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:
 	up_read(&dst_mm->mmap_sem);
 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,
 		     bool *mmap_changing)
 {
 	return __mcopy_atomic(dst_mm, dst_start, src_start, len, false,
 			      mmap_changing);
 }

 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
 		       unsigned long len, bool *mmap_changing)
 {
 	return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing);
 }
	// 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 "internal.h"

	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)
	{
	struct mem_cgroup *memcg;
	pte_t _dst_pte, *dst_pte;
	spinlock_t *ptl;
	void *page_kaddr;
	int ret;
	struct page *page;
	pgoff_t offset, max_off;
	struct inode *inode;

	if (!*pagep) {
	ret = -ENOMEM;
	page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
	if (!page)
	goto out;

	page_kaddr = kmap_atomic(page);
	ret = copy_from_user(page_kaddr,
	(const void __user *) src_addr,
	PAGE_SIZE);
	kunmap_atomic(page_kaddr);

	/* fallback to copy_from_user outside mmap_sem */
	if (unlikely(ret)) {
	ret = -ENOENT;
	*pagep = page;
	/* don't free the page */
	goto out;
	}
	} else {
	page = *pagep;
	*pagep = NULL;
	}

	/*
	* The memory barrier inside __SetPageUptodate makes sure that
	* preceeding stores to the page contents become visible before
	* the set_pte_at() write.
	*/
	__SetPageUptodate(page);

	ret = -ENOMEM;
	if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
	goto out_release;

	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
	if (dst_vma->vm_flags & VM_WRITE)
	_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));

	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_release_uncharge_unlock;
	}
	ret = -EEXIST;
	if (!pte_none(*dst_pte))
	goto out_release_uncharge_unlock;

	inc_mm_counter(dst_mm, MM_ANONPAGES);
	page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
	mem_cgroup_commit_charge(page, memcg, false, false);
	lru_cache_add_active_or_unevictable(page, dst_vma);

	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);

	pte_unmap_unlock(dst_pte, ptl);
	ret = 0;
	out:
	return ret;
	out_release_uncharge_unlock:
	pte_unmap_unlock(dst_pte, ptl);
	mem_cgroup_cancel_charge(page, memcg, false);
	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;
	}

	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_sem held, it will release mmap_sem 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,
	bool zeropage)
	{
	int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
	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;
	struct hstate *h;
	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 (zeropage) {
	up_read(&dst_mm->mmap_sem);
	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_sem and
	* retry, dst_vma will be set to NULL and we must lookup again.
	*/
	if (!dst_vma) {
	err = -ENOENT;
	dst_vma = find_vma(dst_mm, dst_start);
	if (!dst_vma \|\| !is_vm_hugetlb_page(dst_vma))
	goto out_unlock;
	/*
	* 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)
	goto out_unlock;

	if (dst_start < dst_vma->vm_start \|\|
	dst_start + len > dst_vma->vm_end)
	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 (WARN_ON(dst_addr & (vma_hpagesize - 1) \|\|
	(len - copied) & (vma_hpagesize - 1)))
	goto out_unlock;

	/*
	* 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;
	}

	h = hstate_vma(dst_vma);

	while (src_addr < src_start + len) {
	pte_t dst_pteval;

	BUG_ON(dst_addr >= dst_start + len);
	VM_BUG_ON(dst_addr & ~huge_page_mask(h));

	/*
	* Serialize via hugetlb_fault_mutex
	*/
	idx = linear_page_index(dst_vma, dst_addr);
	mapping = dst_vma->vm_file->f_mapping;
	hash = hugetlb_fault_mutex_hash(h, mapping, idx, dst_addr);
	mutex_lock(&hugetlb_fault_mutex_table[hash]);

	err = -ENOMEM;
	dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h));
	if (!dst_pte) {
	mutex_unlock(&hugetlb_fault_mutex_table[hash]);
	goto out_unlock;
	}

	err = -EEXIST;
	dst_pteval = huge_ptep_get(dst_pte);
	if (!huge_pte_none(dst_pteval)) {
	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, &page);

	mutex_unlock(&hugetlb_fault_mutex_table[hash]);
	vm_alloc_shared = vm_shared;

	cond_resched();

	if (unlikely(err == -ENOENT)) {
	up_read(&dst_mm->mmap_sem);
	BUG_ON(!page);

	err = copy_huge_page_from_user(page,
	(const void __user *)src_addr,
	pages_per_huge_page(h), true);
	if (unlikely(err)) {
	err = -EFAULT;
	goto out;
	}
	down_read(&dst_mm->mmap_sem);

	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:
	up_read(&dst_mm->mmap_sem);
	out:
	if (page) {
	/*
	* We encountered an error and are about to free a newly
	* allocated huge page.
	*
	* Reservation handling is very subtle, and is different for
	* private and shared mappings. See the routine
	* restore_reserve_on_error for details. Unfortunately, we
	* can not call restore_reserve_on_error now as it would
	* require holding mmap_sem.
	*
	* If a reservation for the page existed in the reservation
	* map of a private mapping, the map was modified to indicate
	* the reservation was consumed when the page was allocated.
	* We clear the PagePrivate flag now so that the global
	* reserve count will not be incremented in free_huge_page.
	* The reservation map will still indicate the reservation
	* was consumed and possibly prevent later page allocation.
	* This is better than leaking a global reservation. If no
	* reservation existed, it is still safe to clear PagePrivate
	* as no adjustments to reservation counts were made during
	* allocation.
	*
	* The reservation map for shared mappings indicates which
	* pages have reservations. When a huge page is allocated
	* for an address with a reservation, no change is made to
	* the reserve map. In this case PagePrivate will be set
	* to indicate that the global reservation count should be
	* incremented when the page is freed. This is the desired
	* behavior. However, when a huge page is allocated for an
	* address without a reservation a reservation entry is added
	* to the reservation map, and PagePrivate will not be set.
	* When the page is freed, the global reserve count will NOT
	* be incremented and it will appear as though we have leaked
	* reserved page. In this case, set PagePrivate so that the
	* global reserve count will be incremented to match the
	* reservation map entry which was created.
	*
	* Note that vm_alloc_shared is based on the flags of the vma
	* for which the page was originally allocated. dst_vma could
	* be different or NULL on error.
	*/
	if (vm_alloc_shared)
	SetPagePrivate(page);
	else
	ClearPagePrivate(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,
	bool zeropage);
	#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,
	bool zeropage)
	{
	ssize_t err;

	/*
	* 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 (!zeropage)
	err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
	dst_addr, src_addr, page);
	else
	err = mfill_zeropage_pte(dst_mm, dst_pmd,
	dst_vma, dst_addr);
	} else {
	if (!zeropage)
	err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
	dst_vma, dst_addr,
	src_addr, page);
	else
	err = shmem_mfill_zeropage_pte(dst_mm, dst_pmd,
	dst_vma, dst_addr);
	}

	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,
	bool zeropage,
	bool *mmap_changing)
	{
	struct vm_area_struct *dst_vma;
	ssize_t err;
	pmd_t *dst_pmd;
	unsigned long src_addr, dst_addr;
	long copied;
	struct page *page;

	/*
	* 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:
	down_read(&dst_mm->mmap_sem);

	/*
	* 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 && READ_ONCE(*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_vma(dst_mm, dst_start);
	if (!dst_vma)
	goto out_unlock;
	/*
	* 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)
	goto out_unlock;

	if (dst_start < dst_vma->vm_start \|\|
	dst_start + len > dst_vma->vm_end)
	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;

	/*
	* 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, zeropage);

	if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
	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, zeropage);
	cond_resched();

	if (unlikely(err == -ENOENT)) {
	void *page_kaddr;

	up_read(&dst_mm->mmap_sem);
	BUG_ON(!page);

	page_kaddr = kmap(page);
	err = copy_from_user(page_kaddr,
	(const void __user *) src_addr,
	PAGE_SIZE);
	kunmap(page);
	if (unlikely(err)) {
	err = -EFAULT;
	goto out;
	}
	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:
	up_read(&dst_mm->mmap_sem);
	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,
	bool *mmap_changing)
	{
	return __mcopy_atomic(dst_mm, dst_start, src_start, len, false,
	mmap_changing);
	}

	ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
	unsigned long len, bool *mmap_changing)
	{
	return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing);
	}