/*
   *   linux/mm/fremap.c
   * 
   * Explicit pagetable population and nonlinear (random) mappings support.
   *
   * started by Ingo Molnar, Copyright (C) 2002, 2003
   */
  #include <linux/export.h>
  #include <linux/backing-dev.h>
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/file.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/swapops.h>
  #include <linux/rmap.h>
  #include <linux/syscalls.h>
  #include <linux/mmu_notifier.h>
  
  #include <asm/mmu_context.h>
  #include <asm/cacheflush.h>
  #include <asm/tlbflush.h>
  
  #include "internal.h"
  
  static int mm_counter(struct page *page)
  {
  	return PageAnon(page) ? MM_ANONPAGES : MM_FILEPAGES;
  }
  
  static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  			unsigned long addr, pte_t *ptep)
  {
  	pte_t pte = *ptep;
  	struct page *page;
  	swp_entry_t entry;
  
  	if (pte_present(pte)) {
  		flush_cache_page(vma, addr, pte_pfn(pte));
  		pte = ptep_clear_flush(vma, addr, ptep);
  		page = vm_normal_page(vma, addr, pte);
  		if (page) {
  			if (pte_dirty(pte))
  				set_page_dirty(page);
  			update_hiwater_rss(mm);
  			dec_mm_counter(mm, mm_counter(page));
  			page_remove_rmap(page);
  			page_cache_release(page);
  		}
  	} else {	/* zap_pte() is not called when pte_none() */
  		if (!pte_file(pte)) {
  			update_hiwater_rss(mm);
  			entry = pte_to_swp_entry(pte);
  			if (non_swap_entry(entry)) {
  				if (is_migration_entry(entry)) {
  					page = migration_entry_to_page(entry);
  					dec_mm_counter(mm, mm_counter(page));
  				}
  			} else {
  				free_swap_and_cache(entry);
  				dec_mm_counter(mm, MM_SWAPENTS);
  			}
  		}
  		pte_clear_not_present_full(mm, addr, ptep, 0);
  	}
  }
  
  /*
   * Install a file pte to a given virtual memory address, release any
   * previously existing mapping.
   */
  static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  		unsigned long addr, unsigned long pgoff, pgprot_t prot)
  {
  	int err = -ENOMEM;
  	pte_t *pte, ptfile;
  	spinlock_t *ptl;
  
  	pte = get_locked_pte(mm, addr, &ptl);
  	if (!pte)
  		goto out;
  
  	ptfile = pgoff_to_pte(pgoff);
  
  	if (!pte_none(*pte)) {
  		if (pte_present(*pte) && pte_soft_dirty(*pte))
  			pte_file_mksoft_dirty(ptfile);
  		zap_pte(mm, vma, addr, pte);
  	}
  
  	set_pte_at(mm, addr, pte, ptfile);
  	/*
  	 * We don't need to run update_mmu_cache() here because the "file pte"
  	 * being installed by install_file_pte() is not a real pte - it's a
  	 * non-present entry (like a swap entry), noting what file offset should
  	 * be mapped there when there's a fault (in a non-linear vma where
  	 * that's not obvious).
  	 */
  	pte_unmap_unlock(pte, ptl);
  	err = 0;
  out:
  	return err;
  }
  
  int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
  			     unsigned long size, pgoff_t pgoff)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	int err;
  
  	do {
  		err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
  		if (err)
  			return err;
  
  		size -= PAGE_SIZE;
  		addr += PAGE_SIZE;
  		pgoff++;
  	} while (size);
  
  	return 0;
  }
  EXPORT_SYMBOL(generic_file_remap_pages);
  
  /**
   * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
   * @start: start of the remapped virtual memory range
   * @size: size of the remapped virtual memory range
   * @prot: new protection bits of the range (see NOTE)
   * @pgoff: to-be-mapped page of the backing store file
   * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
   *
   * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
   * (shared backing store file).
   *
   * This syscall works purely via pagetables, so it's the most efficient
   * way to map the same (large) file into a given virtual window. Unlike
   * mmap()/mremap() it does not create any new vmas. The new mappings are
   * also safe across swapout.
   *
   * NOTE: the @prot parameter right now is ignored (but must be zero),
   * and the vma's default protection is used. Arbitrary protections
   * might be implemented in the future.
   */
  SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
  		unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
  {
  	struct mm_struct *mm = current->mm;
  	struct address_space *mapping;
  	struct vm_area_struct *vma;
  	int err = -EINVAL;
  	int has_write_lock = 0;
  	vm_flags_t vm_flags = 0;
  
  	if (prot)
  		return err;
  	/*
  	 * Sanitize the syscall parameters:
  	 */
  	start = start & PAGE_MASK;
  	size = size & PAGE_MASK;
  
  	/* Does the address range wrap, or is the span zero-sized? */
  	if (start + size <= start)
  		return err;
  
  	/* Does pgoff wrap? */
  	if (pgoff + (size >> PAGE_SHIFT) < pgoff)
  		return err;
  
  	/* Can we represent this offset inside this architecture's pte's? */
  #if PTE_FILE_MAX_BITS < BITS_PER_LONG
  	if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
  		return err;
  #endif
  
  	/* We need down_write() to change vma->vm_flags. */
  	down_read(&mm->mmap_sem);
   retry:
  	vma = find_vma(mm, start);
  
  	/*
  	 * Make sure the vma is shared, that it supports prefaulting,
  	 * and that the remapped range is valid and fully within
  	 * the single existing vma.
  	 */
  	if (!vma || !(vma->vm_flags & VM_SHARED))
  		goto out;
  
  	if (!vma->vm_ops || !vma->vm_ops->remap_pages)
  		goto out;
  
  	if (start < vma->vm_start || start + size > vma->vm_end)
  		goto out;
  
  	/* Must set VM_NONLINEAR before any pages are populated. */
  	if (!(vma->vm_flags & VM_NONLINEAR)) {
  		/*
  		 * vm_private_data is used as a swapout cursor
  		 * in a VM_NONLINEAR vma.
  		 */
  		if (vma->vm_private_data)
  			goto out;
  
  		/* Don't need a nonlinear mapping, exit success */
  		if (pgoff == linear_page_index(vma, start)) {
  			err = 0;
  			goto out;
  		}
  
  		if (!has_write_lock) {
  get_write_lock:
  			up_read(&mm->mmap_sem);
  			down_write(&mm->mmap_sem);
  			has_write_lock = 1;
  			goto retry;
  		}
  		mapping = vma->vm_file->f_mapping;
  		/*
  		 * page_mkclean doesn't work on nonlinear vmas, so if
  		 * dirty pages need to be accounted, emulate with linear
  		 * vmas.
  		 */
  		if (mapping_cap_account_dirty(mapping)) {
  			unsigned long addr;
  			struct file *file = get_file(vma->vm_file);
  			/* mmap_region may free vma; grab the info now */
  			vm_flags = vma->vm_flags;
  
  			addr = mmap_region(file, start, size, vm_flags, pgoff);
  			fput(file);
  			if (IS_ERR_VALUE(addr)) {
  				err = addr;
  			} else {
  				BUG_ON(addr != start);
  				err = 0;
  			}
  			goto out_freed;
  		}
  		mutex_lock(&mapping->i_mmap_mutex);
  		flush_dcache_mmap_lock(mapping);
  		vma->vm_flags |= VM_NONLINEAR;
  		vma_interval_tree_remove(vma, &mapping->i_mmap);
  		vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
  		flush_dcache_mmap_unlock(mapping);
  		mutex_unlock(&mapping->i_mmap_mutex);
  	}
  
  	if (vma->vm_flags & VM_LOCKED) {
  		/*
  		 * drop PG_Mlocked flag for over-mapped range
  		 */
  		if (!has_write_lock)
  			goto get_write_lock;
  		vm_flags = vma->vm_flags;
  		munlock_vma_pages_range(vma, start, start + size);
  		vma->vm_flags = vm_flags;
  	}
  
  	mmu_notifier_invalidate_range_start(mm, start, start + size);
  	err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
  	mmu_notifier_invalidate_range_end(mm, start, start + size);
  
  	/*
  	 * We can't clear VM_NONLINEAR because we'd have to do
  	 * it after ->populate completes, and that would prevent
  	 * downgrading the lock.  (Locks can't be upgraded).
  	 */
  
  out:
  	if (vma)
  		vm_flags = vma->vm_flags;
  out_freed:
  	if (likely(!has_write_lock))
  		up_read(&mm->mmap_sem);
  	else
  		up_write(&mm->mmap_sem);
  	if (!err && ((vm_flags & VM_LOCKED) || !(flags & MAP_NONBLOCK)))
  		mm_populate(start, size);
  
  	return err;
  }