/* Virtio balloon implementation, inspired by Dor Loar and Marcelo * Tosatti's implementations. * * Copyright 2008 Rusty Russell IBM Corporation * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */ //#define DEBUG #include <linux/virtio.h> #include <linux/virtio_balloon.h> #include <linux/swap.h> #include <linux/kthread.h> #include <linux/freezer.h> #include <linux/delay.h> struct virtio_balloon { struct virtio_device *vdev; struct virtqueue *inflate_vq, *deflate_vq; /* Where the ballooning thread waits for config to change. */ wait_queue_head_t config_change; /* The thread servicing the balloon. */ struct task_struct *thread; /* Waiting for host to ack the pages we released. */ struct completion acked; /* Do we have to tell Host *before* we reuse pages? */ bool tell_host_first; /* The pages we've told the Host we're not using. */ unsigned int num_pages; struct list_head pages; /* The array of pfns we tell the Host about. */ unsigned int num_pfns; u32 pfns[256]; }; static struct virtio_device_id id_table[] = { { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID }, { 0 }, }; static u32 page_to_balloon_pfn(struct page *page) { unsigned long pfn = page_to_pfn(page); BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT); /* Convert pfn from Linux page size to balloon page size. */ return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT); } static void balloon_ack(struct virtqueue *vq) { struct virtio_balloon *vb; unsigned int len; vb = vq->vq_ops->get_buf(vq, &len); if (vb) complete(&vb->acked); } static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) { struct scatterlist sg; sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns); init_completion(&vb->acked); /* We should always be able to add one buffer to an empty queue. */ if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) != 0) BUG(); vq->vq_ops->kick(vq); /* When host has read buffer, this completes via balloon_ack */ wait_for_completion(&vb->acked); } static void fill_balloon(struct virtio_balloon *vb, size_t num) { /* We can only do one array worth at a time. */ num = min(num, ARRAY_SIZE(vb->pfns)); for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) { struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY); if (!page) { if (printk_ratelimit()) dev_printk(KERN_INFO, &vb->vdev->dev, "Out of puff! Can't get %zu pages\n", num); /* Sleep for at least 1/5 of a second before retry. */ msleep(200); break; } vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page); totalram_pages--; vb->num_pages++; list_add(&page->lru, &vb->pages); } /* Didn't get any? Oh well. */ if (vb->num_pfns == 0) return; tell_host(vb, vb->inflate_vq); } static void release_pages_by_pfn(const u32 pfns[], unsigned int num) { unsigned int i; for (i = 0; i < num; i++) { __free_page(pfn_to_page(pfns[i])); totalram_pages++; } } static void leak_balloon(struct virtio_balloon *vb, size_t num) { struct page *page; /* We can only do one array worth at a time. */ num = min(num, ARRAY_SIZE(vb->pfns)); for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) { page = list_first_entry(&vb->pages, struct page, lru); list_del(&page->lru); vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page); vb->num_pages--; } if (vb->tell_host_first) { tell_host(vb, vb->deflate_vq); release_pages_by_pfn(vb->pfns, vb->num_pfns); } else { release_pages_by_pfn(vb->pfns, vb->num_pfns); tell_host(vb, vb->deflate_vq); } } static void virtballoon_changed(struct virtio_device *vdev) { struct virtio_balloon *vb = vdev->priv; wake_up(&vb->config_change); } static inline s64 towards_target(struct virtio_balloon *vb) { u32 v; vb->vdev->config->get(vb->vdev, offsetof(struct virtio_balloon_config, num_pages), &v, sizeof(v)); return (s64)v - vb->num_pages; } static void update_balloon_size(struct virtio_balloon *vb) { __le32 actual = cpu_to_le32(vb->num_pages); vb->vdev->config->set(vb->vdev, offsetof(struct virtio_balloon_config, actual), &actual, sizeof(actual)); } static int balloon(void *_vballoon) { struct virtio_balloon *vb = _vballoon; set_freezable(); while (!kthread_should_stop()) { s64 diff; try_to_freeze(); wait_event_interruptible(vb->config_change, (diff = towards_target(vb)) != 0 || kthread_should_stop() || freezing(current)); if (diff > 0) fill_balloon(vb, diff); else if (diff < 0) leak_balloon(vb, -diff); update_balloon_size(vb); } return 0; } static int virtballoon_probe(struct virtio_device *vdev) { struct virtio_balloon *vb; int err; vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL); if (!vb) { err = -ENOMEM; goto out; } INIT_LIST_HEAD(&vb->pages); vb->num_pages = 0; init_waitqueue_head(&vb->config_change); vb->vdev = vdev; /* We expect two virtqueues. */ vb->inflate_vq = vdev->config->find_vq(vdev, 0, balloon_ack); if (IS_ERR(vb->inflate_vq)) { err = PTR_ERR(vb->inflate_vq); goto out_free_vb; } vb->deflate_vq = vdev->config->find_vq(vdev, 1, balloon_ack); if (IS_ERR(vb->deflate_vq)) { err = PTR_ERR(vb->deflate_vq); goto out_del_inflate_vq; } vb->thread = kthread_run(balloon, vb, "vballoon"); if (IS_ERR(vb->thread)) { err = PTR_ERR(vb->thread); goto out_del_deflate_vq; } vb->tell_host_first = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST); return 0; out_del_deflate_vq: vdev->config->del_vq(vb->deflate_vq); out_del_inflate_vq: vdev->config->del_vq(vb->inflate_vq); out_free_vb: kfree(vb); out: return err; } static void virtballoon_remove(struct virtio_device *vdev) { struct virtio_balloon *vb = vdev->priv; kthread_stop(vb->thread); /* There might be pages left in the balloon: free them. */ while (vb->num_pages) leak_balloon(vb, vb->num_pages); /* Now we reset the device so we can clean up the queues. */ vdev->config->reset(vdev); vdev->config->del_vq(vb->deflate_vq); vdev->config->del_vq(vb->inflate_vq); kfree(vb); } static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST }; static struct virtio_driver virtio_balloon = { .feature_table = features, .feature_table_size = ARRAY_SIZE(features), .driver.name = KBUILD_MODNAME, .driver.owner = THIS_MODULE, .id_table = id_table, .probe = virtballoon_probe, .remove = __devexit_p(virtballoon_remove), .config_changed = virtballoon_changed, }; static int __init init(void) { return register_virtio_driver(&virtio_balloon); } static void __exit fini(void) { unregister_virtio_driver(&virtio_balloon); } module_init(init); module_exit(fini); MODULE_DEVICE_TABLE(virtio, id_table); MODULE_DESCRIPTION("Virtio balloon driver"); MODULE_LICENSE("GPL");