/*
   *  mm/userfaultfd.c
   *
   *  Copyright (C) 2015  Red Hat, Inc.
   *
   *  This work is licensed under the terms of the GNU GPL, version 2. See
   *  the COPYING file in the top-level directory.
   */
  
  #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);

  }