linux/drivers/virtio/virtio_balloon.c
Amit Shah e562966dba virtio: balloon: Add freeze, restore handlers to support S4
Handling balloon hibernate / restore is tricky.  If the balloon was
inflated before going into the hibernation state, upon resume, the host
will not have any memory of that.  Any pages that were passed on to the
host earlier would most likely be invalid, and the host will have to
re-balloon to the previous value to get in the pre-hibernate state.

So the only sane thing for the guest to do here is to discard all the
pages that were put in the balloon.  When to discard the pages is the
next question.

One solution is to deflate the balloon just before writing the image to
the disk (in the freeze() PM callback).  However, asking for pages from
the host just to discard them immediately after seems wasteful of
resources.  Hence, it makes sense to do this by just fudging our
counters soon after wakeup.  This means we don't deflate the balloon
before sleep, and also don't put unnecessary pressure on the host.

This also helps in the thaw case: if the freeze fails for whatever
reason, the balloon should continue to remain in the inflated state.
This was tested by issuing 'swapoff -a' and trying to go into the S4
state.  That fails, and the balloon stays inflated, as expected.  Both
the host and the guest are happy.

Finally, in the restore() callback, we empty the list of pages that were
previously given off to the host, add the appropriate number of pages to
the totalram_pages counter, reset the num_pages counter to 0, and
all is fine.

As a last step, delete the vqs on the freeze callback to prepare for
hibernation, and re-create them in the restore and thaw callbacks to
resume normal operation.

The kthread doesn't race with any operations here, since it's frozen
before the freeze() call and is thawed after the thaw() and restore()
callbacks, so we're safe with that.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2012-01-12 15:44:47 +10:30

445 lines
11 KiB
C

/*
* Virtio balloon implementation, inspired by Dor Laor 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
*/
#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>
#include <linux/slab.h>
#include <linux/module.h>
struct virtio_balloon
{
struct virtio_device *vdev;
struct virtqueue *inflate_vq, *deflate_vq, *stats_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;
/* 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];
/* Memory statistics */
int need_stats_update;
struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
};
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 = virtqueue_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 (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
BUG();
virtqueue_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 |
__GFP_NOMEMALLOC | __GFP_NOWARN);
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--;
}
/*
* Note that if
* virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
* is true, we *have* to do it in this order
*/
tell_host(vb, vb->deflate_vq);
release_pages_by_pfn(vb->pfns, vb->num_pfns);
}
static inline void update_stat(struct virtio_balloon *vb, int idx,
u16 tag, u64 val)
{
BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
vb->stats[idx].tag = tag;
vb->stats[idx].val = val;
}
#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
static void update_balloon_stats(struct virtio_balloon *vb)
{
unsigned long events[NR_VM_EVENT_ITEMS];
struct sysinfo i;
int idx = 0;
all_vm_events(events);
si_meminfo(&i);
update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
pages_to_bytes(events[PSWPIN]));
update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
pages_to_bytes(events[PSWPOUT]));
update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
pages_to_bytes(i.freeram));
update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
pages_to_bytes(i.totalram));
}
/*
* While most virtqueues communicate guest-initiated requests to the hypervisor,
* the stats queue operates in reverse. The driver initializes the virtqueue
* with a single buffer. From that point forward, all conversations consist of
* a hypervisor request (a call to this function) which directs us to refill
* the virtqueue with a fresh stats buffer. Since stats collection can sleep,
* we notify our kthread which does the actual work via stats_handle_request().
*/
static void stats_request(struct virtqueue *vq)
{
struct virtio_balloon *vb;
unsigned int len;
vb = virtqueue_get_buf(vq, &len);
if (!vb)
return;
vb->need_stats_update = 1;
wake_up(&vb->config_change);
}
static void stats_handle_request(struct virtio_balloon *vb)
{
struct virtqueue *vq;
struct scatterlist sg;
vb->need_stats_update = 0;
update_balloon_stats(vb);
vq = vb->stats_vq;
sg_init_one(&sg, vb->stats, sizeof(vb->stats));
if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
BUG();
virtqueue_kick(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
|| vb->need_stats_update
|| kthread_should_stop()
|| freezing(current));
if (vb->need_stats_update)
stats_handle_request(vb);
if (diff > 0)
fill_balloon(vb, diff);
else if (diff < 0)
leak_balloon(vb, -diff);
update_balloon_size(vb);
}
return 0;
}
static int init_vqs(struct virtio_balloon *vb)
{
struct virtqueue *vqs[3];
vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
const char *names[] = { "inflate", "deflate", "stats" };
int err, nvqs;
/*
* We expect two virtqueues: inflate and deflate, and
* optionally stat.
*/
nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
if (err)
return err;
vb->inflate_vq = vqs[0];
vb->deflate_vq = vqs[1];
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
struct scatterlist sg;
vb->stats_vq = vqs[2];
/*
* Prime this virtqueue with one buffer so the hypervisor can
* use it to signal us later.
*/
sg_init_one(&sg, vb->stats, sizeof vb->stats);
if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb, GFP_KERNEL)
< 0)
BUG();
virtqueue_kick(vb->stats_vq);
}
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;
vb->need_stats_update = 0;
err = init_vqs(vb);
if (err)
goto out_free_vb;
vb->thread = kthread_run(balloon, vb, "vballoon");
if (IS_ERR(vb->thread)) {
err = PTR_ERR(vb->thread);
goto out_del_vqs;
}
return 0;
out_del_vqs:
vdev->config->del_vqs(vdev);
out_free_vb:
kfree(vb);
out:
return err;
}
static void __devexit 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_vqs(vdev);
kfree(vb);
}
#ifdef CONFIG_PM
static int virtballoon_freeze(struct virtio_device *vdev)
{
/*
* The kthread is already frozen by the PM core before this
* function is called.
*/
/* Ensure we don't get any more requests from the host */
vdev->config->reset(vdev);
vdev->config->del_vqs(vdev);
return 0;
}
static int virtballoon_thaw(struct virtio_device *vdev)
{
return init_vqs(vdev->priv);
}
static int virtballoon_restore(struct virtio_device *vdev)
{
struct virtio_balloon *vb = vdev->priv;
struct page *page, *page2;
/* We're starting from a clean slate */
vb->num_pages = 0;
/*
* If a request wasn't complete at the time of freezing, this
* could have been set.
*/
vb->need_stats_update = 0;
/* We don't have these pages in the balloon anymore! */
list_for_each_entry_safe(page, page2, &vb->pages, lru) {
list_del(&page->lru);
totalram_pages++;
}
return init_vqs(vdev->priv);
}
#endif
static unsigned int features[] = {
VIRTIO_BALLOON_F_MUST_TELL_HOST,
VIRTIO_BALLOON_F_STATS_VQ,
};
static struct virtio_driver virtio_balloon_driver = {
.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,
#ifdef CONFIG_PM
.freeze = virtballoon_freeze,
.restore = virtballoon_restore,
.thaw = virtballoon_thaw,
#endif
};
static int __init init(void)
{
return register_virtio_driver(&virtio_balloon_driver);
}
static void __exit fini(void)
{
unregister_virtio_driver(&virtio_balloon_driver);
}
module_init(init);
module_exit(fini);
MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio balloon driver");
MODULE_LICENSE("GPL");