From: Peter Bogdanovic <pbogdano@redhat.com>
Date: Fri, 13 Nov 2009 21:36:03 -0500
Subject: [kvm] balloon driver for guests
Message-id: <20091113213044.29856.87370.sendpatchset@squad5-lp1.lab.bos.redhat.com>
Patchwork-id: 21374
O-Subject: [PATCH RHEL5.5 1/1 BZ522629] Provide balloon driver for KVM Guests
	(repost)
Bugzilla: 522629
RH-Acked-by: Dor Laor <dlaor@redhat.com>
RH-Acked-by: Amit Shah <amit.shah@redhat.com>
RH-Acked-by: Christopher Lalancette <clalance@redhat.com>

https://bugzilla.redhat.com/show_bug.cgi?id=522629

Description:
===========
Virtio balloon driver

New feature to provide balloon driver for KVM Guest OSs that support
virtio drivers. Provides the ability to grow or shrink guest OS
memory usage.


kABI Status:
============
No symbols were harmed.

Brew:
=====
Built on all platforms.
https://brewweb.devel.redhat.com/taskinfo?taskID=2002502

Upstream Status:
================
Yes.
commit  6b35e40767c6c1ac783330109ae8e0c09ea6bc82

Test Status:
============
Hollis Blanchard at IBM rebuilt and installed the RHEL5.4 kernel package
with it applied (and the .config addition), loaded it in a RHEL 5.4
guest, and it works as expected.

However, the driver doesn't auto-load, which is true of all virtio drivers in
RHEL 5.4. Red Hat has added custom init script logic to load
other virtio modules in RHEL 5.4 guests, so that logic would need to cover
the virtio balloon PCI device too. For the record, the PCI ID is 1af4:1002.

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index e37f69e..6e4728a 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -23,3 +23,14 @@ config VIRTIO_PCI
 	  that this version of the driver will work with your VMM.
 
 	  If unsure, say M.
+
+config VIRTIO_BALLOON
+	tristate "Virtio balloon driver (EXPERIMENTAL)"
+	select VIRTIO
+	select VIRTIO_RING
+	---help---
+	  This driver supports increasing and decreasing the amount
+	  of memory within a KVM guest.
+
+	  If unsure, say M.
+
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index cc84999..6738c44 100644
--- a/drivers/virtio/Makefile
+++ b/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_VIRTIO_BALLOON) += virtio_balloon.o
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
new file mode 100644
index 0000000..5e2eb6c
--- /dev/null
+++ b/drivers/virtio/virtio_balloon.c
@@ -0,0 +1,301 @@
+/* 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>
+
+static inline void set_freezable(void) {}
+
+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");
diff --git a/include/linux/virtio_balloon.h b/include/linux/virtio_balloon.h
new file mode 100644
index 0000000..8726ff7
--- /dev/null
+++ b/include/linux/virtio_balloon.h
@@ -0,0 +1,23 @@
+#ifndef _LINUX_VIRTIO_BALLOON_H
+#define _LINUX_VIRTIO_BALLOON_H
+/* This header is BSD licensed so anyone can use the definitions to implement
+ * compatible drivers/servers. */
+#include <linux/virtio_config.h>
+
+/* The ID for virtio_balloon */
+#define VIRTIO_ID_BALLOON	5
+
+/* The feature bitmap for virtio balloon */
+#define VIRTIO_BALLOON_F_MUST_TELL_HOST	0 /* Tell before reclaiming pages */
+
+/* Size of a PFN in the balloon interface. */
+#define VIRTIO_BALLOON_PFN_SHIFT 12
+
+struct virtio_balloon_config
+{
+	/* Number of pages host wants Guest to give up. */
+	__le32 num_pages;
+	/* Number of pages we've actually got in balloon. */
+	__le32 actual;
+};
+#endif /* _LINUX_VIRTIO_BALLOON_H */