![Dave Hansen](/assets/img/avatar_default.png)
The virtio balloon driver has a VIRTIO_BALLOON_F_MUST_TELL_HOST feature bit. Whenever the bit is set, the guest kernel must always tell the host before we free pages back to the allocator. Without this feature, we might free a page (and have another user touch it) while the hypervisor is unprepared for it. But, if the bit is _not_ set, we are under no obligation to reverse the order; we're under no obligation to do _anything_. As of now, qemu-kvm defines the bit, but doesn't set it. This patch makes the "tell host first" logic the only case. This should make everybody happy, and reduce the amount of untested or untestable code in the kernel. This _also_ means that we don't have to preserve a pfn list after the pages are freed, which should let us get rid of some temporary storage (vb->pfns) eventually. Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
384 lines
9.7 KiB
C
384 lines
9.7 KiB
C
/* Virtio balloon implementation, inspired by Dor Loar and Marcelo
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* Tosatti's implementations.
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*
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* Copyright 2008 Rusty Russell IBM Corporation
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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//#define DEBUG
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#include <linux/virtio.h>
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#include <linux/virtio_balloon.h>
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#include <linux/swap.h>
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#include <linux/kthread.h>
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#include <linux/freezer.h>
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#include <linux/delay.h>
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#include <linux/slab.h>
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struct virtio_balloon
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{
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struct virtio_device *vdev;
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struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
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/* Where the ballooning thread waits for config to change. */
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wait_queue_head_t config_change;
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/* The thread servicing the balloon. */
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struct task_struct *thread;
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/* Waiting for host to ack the pages we released. */
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struct completion acked;
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/* The pages we've told the Host we're not using. */
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unsigned int num_pages;
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struct list_head pages;
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/* The array of pfns we tell the Host about. */
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unsigned int num_pfns;
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u32 pfns[256];
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/* Memory statistics */
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int need_stats_update;
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struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
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};
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static struct virtio_device_id id_table[] = {
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{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
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{ 0 },
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};
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static u32 page_to_balloon_pfn(struct page *page)
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{
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unsigned long pfn = page_to_pfn(page);
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BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
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/* Convert pfn from Linux page size to balloon page size. */
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return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
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}
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static void balloon_ack(struct virtqueue *vq)
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{
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struct virtio_balloon *vb;
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unsigned int len;
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vb = virtqueue_get_buf(vq, &len);
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if (vb)
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complete(&vb->acked);
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}
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static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
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{
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struct scatterlist sg;
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sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
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init_completion(&vb->acked);
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/* We should always be able to add one buffer to an empty queue. */
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if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
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BUG();
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virtqueue_kick(vq);
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/* When host has read buffer, this completes via balloon_ack */
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wait_for_completion(&vb->acked);
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}
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static void fill_balloon(struct virtio_balloon *vb, size_t num)
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{
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/* We can only do one array worth at a time. */
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num = min(num, ARRAY_SIZE(vb->pfns));
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for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
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struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
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__GFP_NOMEMALLOC | __GFP_NOWARN);
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if (!page) {
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if (printk_ratelimit())
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dev_printk(KERN_INFO, &vb->vdev->dev,
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"Out of puff! Can't get %zu pages\n",
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num);
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/* Sleep for at least 1/5 of a second before retry. */
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msleep(200);
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break;
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}
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vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
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totalram_pages--;
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vb->num_pages++;
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list_add(&page->lru, &vb->pages);
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}
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/* Didn't get any? Oh well. */
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if (vb->num_pfns == 0)
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return;
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tell_host(vb, vb->inflate_vq);
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}
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static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
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{
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unsigned int i;
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for (i = 0; i < num; i++) {
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__free_page(pfn_to_page(pfns[i]));
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totalram_pages++;
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}
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}
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static void leak_balloon(struct virtio_balloon *vb, size_t num)
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{
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struct page *page;
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/* We can only do one array worth at a time. */
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num = min(num, ARRAY_SIZE(vb->pfns));
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for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
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page = list_first_entry(&vb->pages, struct page, lru);
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list_del(&page->lru);
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vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
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vb->num_pages--;
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}
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/*
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* Note that if
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* virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
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* is true, we *have* to do it in this order
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*/
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tell_host(vb, vb->deflate_vq);
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release_pages_by_pfn(vb->pfns, vb->num_pfns);
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}
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static inline void update_stat(struct virtio_balloon *vb, int idx,
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u16 tag, u64 val)
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{
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BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
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vb->stats[idx].tag = tag;
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vb->stats[idx].val = val;
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}
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#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
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static void update_balloon_stats(struct virtio_balloon *vb)
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{
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unsigned long events[NR_VM_EVENT_ITEMS];
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struct sysinfo i;
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int idx = 0;
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all_vm_events(events);
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si_meminfo(&i);
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update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
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pages_to_bytes(events[PSWPIN]));
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update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
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pages_to_bytes(events[PSWPOUT]));
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
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pages_to_bytes(i.freeram));
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
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pages_to_bytes(i.totalram));
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}
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/*
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* While most virtqueues communicate guest-initiated requests to the hypervisor,
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* the stats queue operates in reverse. The driver initializes the virtqueue
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* with a single buffer. From that point forward, all conversations consist of
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* a hypervisor request (a call to this function) which directs us to refill
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* the virtqueue with a fresh stats buffer. Since stats collection can sleep,
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* we notify our kthread which does the actual work via stats_handle_request().
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*/
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static void stats_request(struct virtqueue *vq)
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{
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struct virtio_balloon *vb;
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unsigned int len;
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vb = virtqueue_get_buf(vq, &len);
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if (!vb)
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return;
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vb->need_stats_update = 1;
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wake_up(&vb->config_change);
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}
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static void stats_handle_request(struct virtio_balloon *vb)
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{
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struct virtqueue *vq;
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struct scatterlist sg;
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vb->need_stats_update = 0;
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update_balloon_stats(vb);
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vq = vb->stats_vq;
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sg_init_one(&sg, vb->stats, sizeof(vb->stats));
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if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
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BUG();
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virtqueue_kick(vq);
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}
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static void virtballoon_changed(struct virtio_device *vdev)
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{
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struct virtio_balloon *vb = vdev->priv;
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wake_up(&vb->config_change);
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}
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static inline s64 towards_target(struct virtio_balloon *vb)
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{
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u32 v;
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vb->vdev->config->get(vb->vdev,
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offsetof(struct virtio_balloon_config, num_pages),
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&v, sizeof(v));
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return (s64)v - vb->num_pages;
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}
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static void update_balloon_size(struct virtio_balloon *vb)
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{
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__le32 actual = cpu_to_le32(vb->num_pages);
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vb->vdev->config->set(vb->vdev,
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offsetof(struct virtio_balloon_config, actual),
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&actual, sizeof(actual));
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}
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static int balloon(void *_vballoon)
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{
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struct virtio_balloon *vb = _vballoon;
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set_freezable();
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while (!kthread_should_stop()) {
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s64 diff;
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try_to_freeze();
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wait_event_interruptible(vb->config_change,
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(diff = towards_target(vb)) != 0
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|| vb->need_stats_update
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|| kthread_should_stop()
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|| freezing(current));
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if (vb->need_stats_update)
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stats_handle_request(vb);
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if (diff > 0)
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fill_balloon(vb, diff);
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else if (diff < 0)
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leak_balloon(vb, -diff);
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update_balloon_size(vb);
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}
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return 0;
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}
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static int virtballoon_probe(struct virtio_device *vdev)
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{
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struct virtio_balloon *vb;
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struct virtqueue *vqs[3];
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vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
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const char *names[] = { "inflate", "deflate", "stats" };
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int err, nvqs;
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vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
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if (!vb) {
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err = -ENOMEM;
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goto out;
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}
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INIT_LIST_HEAD(&vb->pages);
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vb->num_pages = 0;
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init_waitqueue_head(&vb->config_change);
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vb->vdev = vdev;
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vb->need_stats_update = 0;
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/* We expect two virtqueues: inflate and deflate,
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* and optionally stat. */
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nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
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err = vdev->config->find_vqs(vdev, nvqs, vqs, callbacks, names);
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if (err)
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goto out_free_vb;
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vb->inflate_vq = vqs[0];
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vb->deflate_vq = vqs[1];
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if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
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struct scatterlist sg;
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vb->stats_vq = vqs[2];
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/*
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* Prime this virtqueue with one buffer so the hypervisor can
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* use it to signal us later.
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*/
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sg_init_one(&sg, vb->stats, sizeof vb->stats);
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if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb) < 0)
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BUG();
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virtqueue_kick(vb->stats_vq);
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}
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vb->thread = kthread_run(balloon, vb, "vballoon");
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if (IS_ERR(vb->thread)) {
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err = PTR_ERR(vb->thread);
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goto out_del_vqs;
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}
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return 0;
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out_del_vqs:
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vdev->config->del_vqs(vdev);
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out_free_vb:
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kfree(vb);
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out:
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return err;
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}
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static void __devexit virtballoon_remove(struct virtio_device *vdev)
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{
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struct virtio_balloon *vb = vdev->priv;
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kthread_stop(vb->thread);
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/* There might be pages left in the balloon: free them. */
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while (vb->num_pages)
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leak_balloon(vb, vb->num_pages);
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/* Now we reset the device so we can clean up the queues. */
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vdev->config->reset(vdev);
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vdev->config->del_vqs(vdev);
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kfree(vb);
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}
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static unsigned int features[] = {
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VIRTIO_BALLOON_F_MUST_TELL_HOST,
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VIRTIO_BALLOON_F_STATS_VQ,
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};
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static struct virtio_driver virtio_balloon_driver = {
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.feature_table = features,
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.feature_table_size = ARRAY_SIZE(features),
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.driver.name = KBUILD_MODNAME,
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.driver.owner = THIS_MODULE,
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.id_table = id_table,
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.probe = virtballoon_probe,
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.remove = __devexit_p(virtballoon_remove),
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.config_changed = virtballoon_changed,
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};
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static int __init init(void)
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{
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return register_virtio_driver(&virtio_balloon_driver);
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}
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static void __exit fini(void)
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{
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unregister_virtio_driver(&virtio_balloon_driver);
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}
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module_init(init);
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module_exit(fini);
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MODULE_DEVICE_TABLE(virtio, id_table);
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MODULE_DESCRIPTION("Virtio balloon driver");
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MODULE_LICENSE("GPL");
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