[PATCH] KVM virtio balloon driver

[Marcelo Tosatti <marcelo@kvack.org>]

Hi Rusty,

It was agreed that the balloon driver should be merged through the
virtio tree, so here it goes. It depends on the config_changed patch
posted earlier.


-----

Following patch adds the KVM balloon driver.

Changes from last version:
- Get rid of global variables/structure
- Use page->lru to link ballooned pages
- Use dev_dbg/dev_printk
- Proper kthread_should_stop handling
- Move shared definitions to separate header
- Use ->config_changed method for notification

This depends on Rusty's config_changed patch.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>


Index: linux-2.6-nv/drivers/virtio/Kconfig
===================================================================
--- linux-2.6-nv.orig/drivers/virtio/Kconfig
+++ linux-2.6-nv/drivers/virtio/Kconfig
@@ -23,3 +23,12 @@ config VIRTIO_PCI
 
 	  If unsure, say M.
 
+config KVM_BALLOON
+	tristate "KVM balloon driver (EXPERIMENTAL)"
+	depends on VIRTIO_PCI
+	---help---
+	 This driver provides support for ballooning memory in/out of a
+	 KVM paravirt guest.	
+
+	 If unsure, say M.
+
Index: linux-2.6-nv/drivers/virtio/Makefile
===================================================================
--- linux-2.6-nv.orig/drivers/virtio/Makefile
+++ linux-2.6-nv/drivers/virtio/Makefile
@@ -1,3 +1,4 @@
 obj-$(CONFIG_VIRTIO) += virtio.o
 obj-$(CONFIG_VIRTIO_RING) += virtio_ring.o
 obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
+obj-$(CONFIG_KVM_BALLOON) += kvm_balloon.o
Index: linux-2.6-nv/drivers/virtio/kvm_balloon.c
===================================================================
--- /dev/null
+++ linux-2.6-nv/drivers/virtio/kvm_balloon.c
@@ -0,0 +1,537 @@
+/*
+ * KVM guest balloon driver
+ *
+ * Copyright (C) 2007, Qumranet, Inc., Dor Laor <dor.laor@qumranet.com>
+ * Copyright (C) 2007, Red Hat, Inc., Marcelo Tosatti <mtosatti@redhat.com>
+ * 
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#define DEBUG
+#include <asm/uaccess.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/wait.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/version.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_balloon.h>
+#include <linux/preempt.h>
+#include <linux/kvm_types.h>
+#include <linux/kvm_host.h>
+
+MODULE_AUTHOR ("Dor Laor");
+MODULE_DESCRIPTION ("Implements guest ballooning support");
+MODULE_LICENSE("GPL");
+MODULE_VERSION("1");
+
+static int kvm_balloon_debug;
+
+#define dprintk(dev, str...) if (kvm_balloon_debug) dev_dbg(dev, str)
+
+#define BALLOON_DATA_SIZE 200
+
+struct balloon_buf {
+	struct virtio_balloon_hdr hdr;
+	u8 data[BALLOON_DATA_SIZE];
+};
+
+struct balloon_work {
+	struct balloon_buf *buf;
+	struct list_head list;
+};
+
+#define VIRTIO_MAX_SG 2
+
+struct virtballoon {
+	struct virtio_device *vdev;
+	struct virtqueue *vq;
+	struct task_struct *balloon_thread;
+	wait_queue_head_t balloon_wait;
+	wait_queue_head_t rmmod_wait;
+	uint32_t target_nrpages;
+	atomic_t inflight_bufs;
+	int balloon_size;
+	struct list_head balloon_plist;
+	struct list_head balloon_work;
+	spinlock_t plist_lock;
+	spinlock_t queue_lock;
+	struct list_head list;
+};
+
+struct balloon_buf *alloc_balloon_buf(struct virtio_device *vdev, gfp_t flags)
+{
+	struct balloon_buf *buf;
+
+	buf = kzalloc(sizeof(struct balloon_buf), flags);
+	if (!buf)
+		dev_printk(KERN_ERR, &vdev->dev, "%s: alloc fail\n", __func__);
+
+	return buf;
+}
+
+static int send_balloon_buf(struct virtballoon *v, uint8_t cmd,
+			    struct balloon_buf *buf)
+{
+	struct scatterlist sg[VIRTIO_MAX_SG];
+	int err = 0;
+
+	buf->hdr.cmd = cmd;
+
+	sg_init_table(sg, VIRTIO_MAX_SG);
+	sg_set_buf(&sg[0], &buf->hdr, sizeof(buf->hdr));
+	sg_set_buf(&sg[1], &buf->data, sizeof(buf->data));
+
+	spin_lock_irq(&v->queue_lock);
+	err = v->vq->vq_ops->add_buf(v->vq, sg, 0, 2, buf);
+	if (err) {
+		dev_printk(KERN_ERR, &v->vq->vdev->dev, "%s: add_buf err\n",
+			   __func__);
+		goto out;
+	}
+
+	/* TODO: kick several balloon buffers at once */
+	v->vq->vq_ops->kick(v->vq);
+out:
+	spin_unlock_irq(&v->queue_lock);
+	atomic_inc(&v->inflight_bufs);
+	return err;
+}
+
+static int kvm_balloon_inflate(struct virtballoon *v, int32_t npages)
+{
+	LIST_HEAD(tmp_list);
+	struct page *page, *tmp;
+	struct balloon_buf *buf;
+	u32 *pfn;
+	int allocated = 0;
+	int i, r = -ENOMEM;
+
+	buf = alloc_balloon_buf(v->vdev, GFP_KERNEL);
+	if (!buf)
+		return r;
+
+	pfn = (u32 *)&buf->data;
+	*pfn++ = (u32)npages;
+
+	for (i = 0; i < npages; i++) {
+		page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
+		if (!page)
+			goto out_free;
+		list_add(&page->lru, &tmp_list);
+		allocated++;
+		*pfn = page_to_pfn(page);
+		pfn++;
+	}
+
+	r = send_balloon_buf(v, CMD_BALLOON_INFLATE, buf);
+	if (r)
+		goto out_free;
+
+	spin_lock(&v->plist_lock);
+	list_splice(&tmp_list, &v->balloon_plist);
+	v->balloon_size += allocated;
+	totalram_pages -= allocated;
+	dprintk(&v->vdev->dev, "%s: current balloon size=%d\n", __func__,
+		v->balloon_size);
+	spin_unlock(&v->plist_lock);
+	return allocated;
+
+out_free:
+	list_for_each_entry_safe(page, tmp, &tmp_list, lru) {
+		list_del(&page->lru);
+		__free_page(page);
+	}
+	return r;
+}
+
+static int kvm_balloon_deflate(struct virtballoon *v, int32_t npages)
+{
+	LIST_HEAD(tmp_list);
+	struct page *page, *tmp;
+	struct balloon_buf *buf;
+	u32 *pfn;
+	int deallocated = 0;
+	int r = 0;
+
+	buf = alloc_balloon_buf(v->vdev, GFP_KERNEL);
+	if (!buf)
+		return r;
+
+	spin_lock(&v->plist_lock);
+
+	if (v->balloon_size < npages) {
+		dev_printk(KERN_INFO, &v->vdev->dev,
+			   "%s: balloon=%d with deflate rq=%d\n",
+			   __func__, v->balloon_size, npages);
+		npages = v->balloon_size;
+		if (!npages)
+			goto out;
+	}
+
+	pfn = (u32 *)&buf->data;
+	*pfn++ = (u32)-npages;
+
+	/*
+	 * Move the balloon pages to tmp list before issuing 
+	 * the virtio buffer
+	 */
+	list_for_each_entry_safe(page, tmp, &v->balloon_plist, lru) {
+		*pfn++ = page_to_pfn(page);
+		list_move(&page->lru, &tmp_list);
+		if (++deallocated == npages)
+			break;
+	}
+
+	r = send_balloon_buf(v, CMD_BALLOON_DEFLATE, buf);
+	if (r)
+		goto out;
+
+	list_for_each_entry_safe(page, tmp, &tmp_list, lru)
+		list_del_init(&page->lru);
+
+	v->balloon_size -= npages;
+	totalram_pages += npages;
+	dprintk(&v->vdev->dev, "%s: current balloon size=%d\n", __func__,
+	       v->balloon_size);
+
+	spin_unlock(&v->plist_lock);
+	return deallocated;
+
+out:
+	list_splice(&tmp_list, &v->balloon_plist);
+	spin_unlock(&v->plist_lock);
+	return r;
+}
+
+#define MAX_BALLOON_PAGES_PER_OP (BALLOON_DATA_SIZE/sizeof(u32)) \
+				 - sizeof(int32_t)
+#define MAX_BALLOON_XFLATE_OP 1000000
+
+static int kvm_balloon_xflate(struct virtballoon *v, int32_t npages)
+{
+	int r = -EINVAL, i;
+	int iterations;
+	int abspages;
+	int curr_pages = 0;
+	int gfns_per_buf;
+
+	abspages = abs(npages);
+
+	if (abspages > MAX_BALLOON_XFLATE_OP) {
+		dev_printk(KERN_ERR, &v->vdev->dev,
+			   "%s: bad npages=%d\n", __func__, npages);
+		return -EINVAL;
+	}
+
+	dprintk(&v->vdev->dev, "%s: got %s, npages=%d\n", __func__,
+	       (npages > 0)? "inflate":"deflate", npages);
+
+	gfns_per_buf = MAX_BALLOON_PAGES_PER_OP;
+
+	/*
+	 * Call the balloon in PAGE_SIZE*pfns-per-buf
+	 * iterations
+	 */
+	iterations = DIV_ROUND_UP(abspages, gfns_per_buf);
+	dprintk(&v->vdev->dev, "%s: iterations=%d\n", __func__, iterations);
+
+	for (i = 0; i < iterations; i++) {
+		int32_t pages_in_iteration = 
+			min(abspages - curr_pages, gfns_per_buf);
+
+		if (npages > 0)
+			r = kvm_balloon_inflate(v, pages_in_iteration);
+		else
+			r = kvm_balloon_deflate(v, pages_in_iteration);
+						
+		if (r < 0)
+			return r;
+		curr_pages += r;
+		if (r != pages_in_iteration)
+			break;
+		cond_resched();
+	}
+
+	return curr_pages;
+}
+
+static void inflate_done(struct virtballoon *v, struct balloon_buf *buf)
+{
+	uint8_t status = buf->hdr.status;
+
+	/* error inflating, return pages to the system */
+	if (status) {
+	 	struct page *page;
+		u32 *pfn = (u32 *)&buf->data;
+		int npages = (int)*pfn++;
+		int i;
+
+		spin_lock(&v->plist_lock);
+		for (i=0;i<npages;i++) { 	
+			page = pfn_to_page(*pfn);
+			list_del_init(&page->lru);
+			__free_page(page);
+			v->balloon_size--;
+			totalram_pages++;
+			v->target_nrpages++;
+			pfn++;
+		}
+		spin_unlock(&v->plist_lock);
+	}
+}
+
+static void deflate_done(struct virtballoon *v, struct balloon_buf *buf)
+{
+	uint8_t status = buf->hdr.status;
+
+	/* deflate OK, return pages to the system */
+	if (!status) { 
+		u32 *pfn = (u32 *)&buf->data;
+		int npages, i;
+
+		npages = (int)*pfn++;
+		npages = abs(npages);
+
+		for (i = 0; i<npages; i++) {
+			__free_page(pfn_to_page(*pfn));
+			pfn++;
+		}
+	/* deflate error, add pages back to ballooned list */
+	} else {
+		u32 *pfn = (u32 *)&buf->data;
+		int npages, i;
+		struct page *page;
+
+		npages = (int)*pfn++;
+		npages = abs(npages);
+
+		spin_lock(&v->plist_lock);
+		for (i = 0; i < npages; i++) {
+			page = pfn_to_page(*pfn++);
+			list_add(&page->lru, &v->balloon_plist);
+			v->balloon_size++;
+			totalram_pages--;
+			v->target_nrpages--;
+		}
+		spin_unlock(&v->plist_lock);
+	}
+	return;
+}
+
+static int balloon_thread(void *p)
+{
+	struct virtballoon *v = p;
+	DEFINE_WAIT(wait);
+	int rmmod = 0;
+
+	set_freezable();
+	while (!kthread_should_stop()) {
+		int delta;
+
+		prepare_to_wait(&v->balloon_wait, &wait, TASK_INTERRUPTIBLE);
+		schedule();
+		finish_wait(&v->balloon_wait, &wait);
+
+		try_to_freeze();
+
+		/* wait for kthread_stop() if rmmod has been called */
+		if (rmmod)
+			continue;
+
+		spin_lock_irq(&v->plist_lock);
+		delta = totalram_pages - v->target_nrpages;
+		spin_unlock_irq(&v->plist_lock);
+
+		if (delta)
+			kvm_balloon_xflate(v, delta);
+
+		spin_lock_irq(&v->queue_lock);
+		while (!list_empty(&v->balloon_work)) {
+			struct balloon_work *work;
+			struct balloon_buf *buf;
+
+			work = list_entry(v->balloon_work.next,
+					 struct balloon_work, list);
+			list_del(&work->list);
+			spin_unlock_irq(&v->queue_lock);
+			buf = work->buf;
+			kfree(work);
+
+			switch(buf->hdr.cmd) {
+			case CMD_BALLOON_DEFLATE:
+				deflate_done(v, buf);
+				break;
+			case CMD_BALLOON_INFLATE:
+				inflate_done(v, buf);
+				break;
+			default:
+				printk("%s: unknown cmd 0x%x\n", __func__,
+					buf->hdr.cmd);
+			}
+			kfree(buf);
+			if (atomic_dec_and_test(&v->inflight_bufs)) {
+				if (waitqueue_active(&v->rmmod_wait)) {
+					wake_up(&v->rmmod_wait);
+					rmmod = 1;
+				}
+			}
+			cond_resched();
+			spin_lock_irq(&v->queue_lock);
+		}
+		spin_unlock_irq(&v->queue_lock);
+	}
+	return 0;
+}
+
+static bool balloon_tx_done(struct virtqueue *vq)
+{
+	struct balloon_buf *buf;
+	struct virtballoon *v = vq->vdev->priv;
+	unsigned int len;
+
+	spin_lock(&v->queue_lock);
+	while ((buf = vq->vq_ops->get_buf(vq, &len)) != NULL) {
+		struct balloon_work *work;
+
+		work = kzalloc(sizeof(struct balloon_work), GFP_ATOMIC);
+		if (!work)
+			continue;
+		INIT_LIST_HEAD(&work->list);
+		work->buf = buf;
+
+		list_add(&work->list, &v->balloon_work);
+	}
+	spin_unlock(&v->queue_lock);
+	wake_up(&v->balloon_wait);
+
+	return true;
+}
+
+static struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID},
+	{ 0 },
+};
+
+static LIST_HEAD(balloon_devices);
+
+static int balloon_probe(struct virtio_device *vdev)
+{
+	int err = -EINVAL;
+	struct virtballoon *v;
+
+	v = kzalloc(GFP_KERNEL, sizeof(struct virtballoon));
+	if (!v)
+		return -ENOMEM;
+
+	v->vq = vdev->config->find_vq(vdev, 0, balloon_tx_done);
+	if (IS_ERR(v->vq))
+		goto out_free;
+	
+	v->vdev = vdev;
+
+	init_waitqueue_head(&v->balloon_wait);
+	init_waitqueue_head(&v->rmmod_wait);
+	spin_lock_init(&v->plist_lock);
+	spin_lock_init(&v->queue_lock);
+	INIT_LIST_HEAD(&v->balloon_plist);
+	INIT_LIST_HEAD(&v->balloon_work);
+	INIT_LIST_HEAD(&v->list);
+	atomic_set(&v->inflight_bufs, 0);
+
+	vdev->priv = v;
+
+	v->balloon_thread = kthread_run(balloon_thread, v, "kvm_balloond");
+	if (IS_ERR(v->balloon_thread)) 
+		goto out_free_vq;
+
+	list_add(&v->list, &balloon_devices);
+
+	dev_printk(KERN_INFO, &v->vdev->dev, "registered\n");
+
+	return 0;
+
+out_free_vq:
+	vdev->config->del_vq(v->vq);
+out_free:
+	kfree(v);
+	return err;
+}
+
+static void balloon_remove(struct virtio_device *vdev)
+{
+	struct virtballoon *v = vdev->priv;
+
+	kthread_stop(v->balloon_thread);
+	vdev->config->del_vq(v->vq);
+	list_del(&v->list);
+	kfree(v);
+}
+
+static void balloon_config_changed(struct virtio_device *vdev)
+{
+	struct virtballoon *v = vdev->priv;
+
+	spin_lock(&v->plist_lock);
+	__virtio_config_val(v->vdev, 0, &v->target_nrpages);
+	spin_unlock(&v->plist_lock);
+	wake_up(&v->balloon_wait);
+	dprintk(&vdev->dev, "%s\n", __func__);
+}
+
+static struct virtio_driver virtio_balloon = {
+	.driver.name =  KBUILD_MODNAME,
+	.driver.owner = THIS_MODULE,
+	.id_table =     id_table,
+	.probe =        balloon_probe,
+	.remove =	__devexit_p(balloon_remove),
+	.config_changed	= balloon_config_changed,
+};
+
+module_param(kvm_balloon_debug, int, 0);
+
+static int __init kvm_balloon_init(void)
+{
+	return register_virtio_driver(&virtio_balloon);
+}
+
+static void __exit kvm_balloon_exit(void)
+{
+	struct virtballoon *v;
+	
+	list_for_each_entry(v, &balloon_devices, list) { 
+		spin_lock(&v->plist_lock);
+		if (v->balloon_size) {
+			DEFINE_WAIT(wait);
+
+			v->target_nrpages += v->balloon_size;
+			spin_unlock(&v->plist_lock);
+			wake_up(&v->balloon_wait);
+			prepare_to_wait(&v->rmmod_wait, &wait,
+					TASK_INTERRUPTIBLE);
+			schedule();
+			finish_wait(&v->rmmod_wait, &wait);
+			spin_lock(&v->plist_lock);
+		}
+
+		if (v->balloon_size)
+			dev_printk(KERN_ERR, &v->vdev->dev,
+				   "%s: exit while balloon not empty!\n",
+				    __func__);
+
+		spin_unlock(&v->plist_lock);
+	}
+
+	unregister_virtio_driver(&virtio_balloon);
+}
+
+module_init(kvm_balloon_init);
+module_exit(kvm_balloon_exit);
Index: linux-2.6-nv/drivers/virtio/virtio_pci.c
===================================================================
--- linux-2.6-nv.orig/drivers/virtio/virtio_pci.c
+++ linux-2.6-nv/drivers/virtio/virtio_pci.c
@@ -67,6 +67,7 @@ static struct pci_device_id virtio_pci_i
 	{ 0x1AF4, 0x1000, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Dummy entry */
 	{ 0x1AF4, 0x1001, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Dummy entry */
 	{ 0x1AF4, 0x1002, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Dummy entry */
+	{ 0x1AF4, 0x1003, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, /* Balloon */
 	{ 0 },
 };
 
Index: linux-2.6-nv/include/linux/virtio_balloon.h
===================================================================
--- /dev/null
+++ linux-2.6-nv/include/linux/virtio_balloon.h
@@ -0,0 +1,20 @@
+#ifndef _LINUX_VIRTIO_BALLOON_H
+#define _LINUX_VIRTIO_BALLOON_H
+#include <linux/virtio_config.h>
+
+#define VIRTIO_ID_BALLOON 3
+
+#define CMD_BALLOON_INFLATE 0x1
+#define CMD_BALLOON_DEFLATE 0x2
+
+struct virtio_balloon_hdr {
+	uint8_t cmd;
+	uint8_t status;
+};
+
+struct virtio_balloon_config
+{
+	uint32_t target_nrpages;
+};
+
+#endif /* _LINUX_VIRTIO_BALLOON_H */