1 files changed, 171 insertions, 63 deletions

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 9075aa54e955..03c5dbabb156 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * mm/balloon_compaction.c
  *
@@ -10,87 +11,180 @@
 #include <linux/export.h>
 #include <linux/balloon_compaction.h>
 
-/*
- * balloon_page_enqueue - allocates a new page and inserts it into the balloon
- *			  page list.
- * @b_dev_info: balloon device descriptor where we will insert a new page to
- *
- * Driver must call it to properly allocate a new enlisted balloon page
- * before definitively removing it from the guest system.
- * This function returns the page address for the recently enqueued page or
- * NULL in the case we fail to allocate a new page this turn.
- */
-struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
+static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
+				     struct page *page)
 {
-	unsigned long flags;
-	struct page *page = alloc_page(balloon_mapping_gfp_mask() |
-				__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_ZERO);
-	if (!page)
-		return NULL;
-
 	/*
 	 * 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.
+	 * 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));
-	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	balloon_page_insert(b_dev_info, page);
+	unlock_page(page);
 	__count_vm_event(BALLOON_INFLATE);
+	inc_node_page_state(page, NR_BALLOON_PAGES);
+}
+
+/**
+ * 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);
-	unlock_page(page);
-	return page;
+	return n_pages;
 }
-EXPORT_SYMBOL_GPL(balloon_page_enqueue);
+EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
 
-/*
- * balloon_page_dequeue - removes a page from balloon's page list and returns
- *			  the its address to allow the driver release the page.
- * @b_dev_info: balloon device decriptor where we will grab a page from.
- *
- * Driver must call it to properly de-allocate a previous enlisted balloon page
- * before definetively releasing it back to the guest system.
- * This function returns the page address for the recently dequeued page or
- * NULL in the case we find balloon's page list temporarily empty due to
- * compaction isolated pages.
+/**
+ * balloon_page_list_dequeue() - removes pages from balloon's page list and
+ *				 returns a list of the pages.
+ * @b_dev_info: balloon device descriptor 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.
  */
-struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
+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;
-	bool dequeued_page;
+	size_t n_pages = 0;
 
-	dequeued_page = false;
 	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
+		 * 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)) {
-#ifdef CONFIG_BALLOON_COMPACTION
-			if (PageIsolated(page)) {
-				/* raced with isolation */
-				unlock_page(page);
-				continue;
-			}
-#endif
-			balloon_page_delete(page);
-			__count_vm_event(BALLOON_DEFLATE);
-			unlock_page(page);
-			dequeued_page = true;
-			break;
-		}
+		if (!trylock_page(page))
+			continue;
+
+		list_del(&page->lru);
+		balloon_page_finalize(page);
+		__count_vm_event(BALLOON_DEFLATE);
+		list_add(&page->lru, pages);
+		unlock_page(page);
+		dec_node_page_state(page, NR_BALLOON_PAGES);
+		n_pages++;
 	}
 	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 
-	if (!dequeued_page) {
+	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 descriptor 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 is no isolated pages, then something
+		 * 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 into
+		 * 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);
@@ -98,20 +192,23 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
 			     !b_dev_info->isolated_pages))
 			BUG();
 		spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
-		page = NULL;
+		return NULL;
 	}
-	return page;
+	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)
+static 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;
 
+	if (!b_dev_info)
+		return false;
+
 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	list_del(&page->lru);
 	b_dev_info->isolated_pages++;
@@ -120,21 +217,23 @@ bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
 	return true;
 }
 
-void balloon_page_putback(struct page *page)
+static void balloon_page_putback(struct page *page)
 {
 	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 	unsigned long flags;
 
+	/* Isolated balloon pages cannot get deflated. */
+	if (WARN_ON_ONCE(!b_dev_info))
+		return;
+
 	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,
+static int balloon_page_migrate(struct page *newpage, struct page *page,
 		enum migrate_mode mode)
 {
 	struct balloon_dev_info *balloon = balloon_page_device(page);
@@ -142,14 +241,23 @@ int balloon_page_migrate(struct address_space *mapping,
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
+	/* Isolated balloon pages cannot get deflated. */
+	if (WARN_ON_ONCE(!balloon))
+		return -EAGAIN;
+
 	return balloon->migratepage(balloon, newpage, page, mode);
 }
 
-const struct address_space_operations balloon_aops = {
-	.migratepage = balloon_page_migrate,
+const struct movable_operations balloon_mops = {
+	.migrate_page = balloon_page_migrate,
 	.isolate_page = balloon_page_isolate,
 	.putback_page = balloon_page_putback,
 };
-EXPORT_SYMBOL_GPL(balloon_aops);
+
+static int __init balloon_init(void)
+{
+	return set_movable_ops(&balloon_mops, PGTY_offline);
+}
+core_initcall(balloon_init);
 
 #endif /* CONFIG_BALLOON_COMPACTION */