1 files changed, 260 insertions, 0 deletions
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
new file mode 100644
index 000000000..26de020aa
--- /dev/null
+++ b/mm/balloon_compaction.c
@@ -0,0 +1,260 @@
+// 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 */