// 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 */