// SPDX-License-Identifier: GPL-2.0-only

  /*
   * mm/balloon_compaction.c
   *
   * Common interface for making balloon pages movable by compaction.
   *
   * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com>
   */
  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <linux/export.h>
  #include <linux/balloon_compaction.h>

  static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
  				     struct page *page)
  {
  	/*
  	 * Block others from accessing the 'page' when we get around to
  	 * establishing additional references. We should be the only one
  	 * holding a reference to the 'page' at this point. If we are not, then
  	 * memory corruption is possible and we should stop execution.
  	 */
  	BUG_ON(!trylock_page(page));

  	balloon_page_insert(b_dev_info, page);
  	unlock_page(page);
  	__count_vm_event(BALLOON_INFLATE);
  }
  
  /**
   * balloon_page_list_enqueue() - inserts a list of pages into the balloon page
   *				 list.
   * @b_dev_info: balloon device descriptor where we will insert a new page to
   * @pages: pages to enqueue - allocated using balloon_page_alloc.
   *

   * Driver must call this function to properly enqueue balloon pages before
   * definitively removing them from the guest system.

   *
   * Return: number of pages that were enqueued.
   */
  size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
  				 struct list_head *pages)
  {
  	struct page *page, *tmp;
  	unsigned long flags;
  	size_t n_pages = 0;
  
  	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  	list_for_each_entry_safe(page, tmp, pages, lru) {

  		list_del(&page->lru);

  		balloon_page_enqueue_one(b_dev_info, page);
  		n_pages++;
  	}
  	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
  	return n_pages;
  }
  EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
  
  /**
   * balloon_page_list_dequeue() - removes pages from balloon's page list and
   *				 returns a list of the pages.
   * @b_dev_info: balloon device decriptor where we will grab a page from.
   * @pages: pointer to the list of pages that would be returned to the caller.
   * @n_req_pages: number of requested pages.
   *
   * Driver must call this function to properly de-allocate a previous enlisted

   * balloon pages before definitively releasing it back to the guest system.

   * This function tries to remove @n_req_pages from the ballooned pages and
   * return them to the caller in the @pages list.
   *

   * Note that this function may fail to dequeue some pages even if the balloon
   * isn't empty - since the page list can be temporarily empty due to compaction
   * of isolated pages.

   *
   * Return: number of pages that were added to the @pages list.
   */
  size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
  				 struct list_head *pages, size_t n_req_pages)
  {
  	struct page *page, *tmp;
  	unsigned long flags;
  	size_t n_pages = 0;
  
  	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  	list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
  		if (n_pages == n_req_pages)
  			break;
  
  		/*
  		 * Block others from accessing the 'page' while we get around to
  		 * establishing additional references and preparing the 'page'
  		 * to be released by the balloon driver.
  		 */
  		if (!trylock_page(page))
  			continue;
  
  		if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&
  		    PageIsolated(page)) {
  			/* raced with isolation */
  			unlock_page(page);
  			continue;
  		}
  		balloon_page_delete(page);
  		__count_vm_event(BALLOON_DEFLATE);
  		list_add(&page->lru, pages);
  		unlock_page(page);
  		n_pages++;
  	}
  	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
  
  	return n_pages;
  }
  EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);

  /*

   * balloon_page_alloc - allocates a new page for insertion into the balloon

   *			page list.

   *

   * Driver must call this function to properly allocate a new balloon page.
   * Driver must call balloon_page_enqueue before definitively removing the page
   * from the guest system.
   *
   * Return: struct page for the allocated page or NULL on allocation failure.

   */
  struct page *balloon_page_alloc(void)
  {
  	struct page *page = alloc_page(balloon_mapping_gfp_mask() |

  				       __GFP_NOMEMALLOC | __GFP_NORETRY |
  				       __GFP_NOWARN);

  	return page;
  }
  EXPORT_SYMBOL_GPL(balloon_page_alloc);
  
  /*

   * balloon_page_enqueue - inserts a new page into the balloon page list.
   *

   * @b_dev_info: balloon device descriptor where we will insert a new page

   * @page: new page to enqueue - allocated using balloon_page_alloc.

   *

   * Drivers must call this function to properly enqueue a new allocated balloon
   * page before definitively removing the page from the guest system.

   *

   * Drivers must not call balloon_page_enqueue on pages that have been pushed to
   * a list with balloon_page_push before removing them with balloon_page_pop. To
   * enqueue a list of pages, use balloon_page_list_enqueue instead.

   */

  void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
  			  struct page *page)

  {
  	unsigned long flags;

  	spin_lock_irqsave(&b_dev_info->pages_lock, flags);

  	balloon_page_enqueue_one(b_dev_info, page);

  	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

  }
  EXPORT_SYMBOL_GPL(balloon_page_enqueue);
  
  /*
   * balloon_page_dequeue - removes a page from balloon's page list and returns

   *			  its address to allow the driver to release the page.

   * @b_dev_info: balloon device decriptor where we will grab a page from.
   *

   * Driver must call this function to properly dequeue a previously enqueued page
   * before definitively releasing it back to the guest system.
   *
   * Caller must perform its own accounting to ensure that this
   * function is called only if some pages are actually enqueued.
   *
   * Note that this function may fail to dequeue some pages even if there are
   * some enqueued pages - since the page list can be temporarily empty due to
   * the compaction of isolated pages.
   *
   * TODO: remove the caller accounting requirements, and allow caller to wait
   * until all pages can be dequeued.
   *
   * Return: struct page for the dequeued page, or NULL if no page was dequeued.

   */
  struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
  {

  	unsigned long flags;

  	LIST_HEAD(pages);
  	int n_pages;

  	n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);

  	if (n_pages != 1) {

  		/*
  		 * If we are unable to dequeue a balloon page because the page

  		 * list is empty and there are no isolated pages, then something

  		 * went out of track and some balloon pages are lost.

  		 * BUG() here, otherwise the balloon driver may get stuck in

  		 * an infinite loop while attempting to release all its pages.
  		 */
  		spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  		if (unlikely(list_empty(&b_dev_info->pages) &&
  			     !b_dev_info->isolated_pages))
  			BUG();
  		spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

  		return NULL;

  	}

  	return list_first_entry(&pages, struct page, lru);

  }
  EXPORT_SYMBOL_GPL(balloon_page_dequeue);
  
  #ifdef CONFIG_BALLOON_COMPACTION

  bool balloon_page_isolate(struct page *page, isolate_mode_t mode)

  {

  	struct balloon_dev_info *b_dev_info = balloon_page_device(page);

  	unsigned long flags;

  	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  	list_del(&page->lru);
  	b_dev_info->isolated_pages++;
  	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

  
  	return true;

  }

  void balloon_page_putback(struct page *page)

  {

  	struct balloon_dev_info *b_dev_info = balloon_page_device(page);

  	unsigned long flags;

  	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
  	list_add(&page->lru, &b_dev_info->pages);
  	b_dev_info->isolated_pages--;
  	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
  }

  
  /* move_to_new_page() counterpart for a ballooned page */

  int balloon_page_migrate(struct address_space *mapping,
  		struct page *newpage, struct page *page,
  		enum migrate_mode mode)

  {

  	struct balloon_dev_info *balloon = balloon_page_device(page);

  	/*
  	 * We can not easily support the no copy case here so ignore it as it

  	 * is unlikely to be used with balloon pages. See include/linux/hmm.h
  	 * for a user of the MIGRATE_SYNC_NO_COPY mode.

  	 */
  	if (mode == MIGRATE_SYNC_NO_COPY)
  		return -EINVAL;

  	VM_BUG_ON_PAGE(!PageLocked(page), page);
  	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);

  	return balloon->migratepage(balloon, newpage, page, mode);
  }

  const struct address_space_operations balloon_aops = {
  	.migratepage = balloon_page_migrate,
  	.isolate_page = balloon_page_isolate,
  	.putback_page = balloon_page_putback,
  };
  EXPORT_SYMBOL_GPL(balloon_aops);

  #endif /* CONFIG_BALLOON_COMPACTION */