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* Virtio Balloon Device
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* Copyright IBM, Corp. 2008
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* Copyright (C) 2011 Red Hat, Inc.
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* Copyright (C) 2011 Amit Shah <amit.shah@redhat.com>
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* Anthony Liguori <aliguori@us.ibm.com>
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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#include "qemu-common.h"
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#include "virtio-balloon.h"
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#if defined(__linux__)
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/* Disable guest-provided stats by now (https://bugzilla.redhat.com/show_bug.cgi?id=623903) */
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#define ENABLE_GUEST_STATS 0
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typedef struct VirtIOBalloon
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VirtQueue *ivq, *dvq, *svq;
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uint64_t stats[VIRTIO_BALLOON_S_NR];
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VirtQueueElement stats_vq_elem;
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size_t stats_vq_offset;
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MonitorCompletion *stats_callback;
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void *stats_opaque_callback_data;
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static VirtIOBalloon *to_virtio_balloon(VirtIODevice *vdev)
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return (VirtIOBalloon *)vdev;
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static void balloon_page(void *addr, int deflate)
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#if defined(__linux__)
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if (!kvm_enabled() || kvm_has_sync_mmu())
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qemu_madvise(addr, TARGET_PAGE_SIZE,
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deflate ? QEMU_MADV_WILLNEED : QEMU_MADV_DONTNEED);
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* reset_stats - Mark all items in the stats array as unset
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* This function needs to be called at device intialization and before
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* before updating to a set of newly-generated stats. This will ensure that no
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* stale values stick around in case the guest reports a subset of the supported
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static inline void reset_stats(VirtIOBalloon *dev)
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for (i = 0; i < VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
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static void stat_put(QDict *dict, const char *label, uint64_t val)
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qdict_put(dict, label, qint_from_int(val));
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static QObject *get_stats_qobject(VirtIOBalloon *dev)
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QDict *dict = qdict_new();
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uint64_t actual = ram_size - ((uint64_t) dev->actual <<
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VIRTIO_BALLOON_PFN_SHIFT);
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stat_put(dict, "actual", actual);
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#if ENABLE_GUEST_STATS
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stat_put(dict, "mem_swapped_in", dev->stats[VIRTIO_BALLOON_S_SWAP_IN]);
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stat_put(dict, "mem_swapped_out", dev->stats[VIRTIO_BALLOON_S_SWAP_OUT]);
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stat_put(dict, "major_page_faults", dev->stats[VIRTIO_BALLOON_S_MAJFLT]);
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stat_put(dict, "minor_page_faults", dev->stats[VIRTIO_BALLOON_S_MINFLT]);
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stat_put(dict, "free_mem", dev->stats[VIRTIO_BALLOON_S_MEMFREE]);
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stat_put(dict, "total_mem", dev->stats[VIRTIO_BALLOON_S_MEMTOT]);
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return QOBJECT(dict);
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static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
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VirtIOBalloon *s = to_virtio_balloon(vdev);
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VirtQueueElement elem;
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while (virtqueue_pop(vq, &elem)) {
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while (iov_to_buf(elem.out_sg, elem.out_num, &pfn, offset, 4) == 4) {
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pa = (ram_addr_t)ldl_p(&pfn) << VIRTIO_BALLOON_PFN_SHIFT;
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addr = cpu_get_physical_page_desc(pa);
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if ((addr & ~TARGET_PAGE_MASK) != IO_MEM_RAM)
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/* Using qemu_get_ram_ptr is bending the rules a bit, but
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should be OK because we only want a single page. */
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balloon_page(qemu_get_ram_ptr(addr), !!(vq == s->dvq));
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virtqueue_push(vq, &elem, offset);
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virtio_notify(vdev, vq);
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static void complete_stats_request(VirtIOBalloon *vb)
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if (!vb->stats_opaque_callback_data)
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stats = get_stats_qobject(vb);
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vb->stats_callback(vb->stats_opaque_callback_data, stats);
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qobject_decref(stats);
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vb->stats_opaque_callback_data = NULL;
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vb->stats_callback = NULL;
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static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
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VirtIOBalloon *s = DO_UPCAST(VirtIOBalloon, vdev, vdev);
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VirtQueueElement *elem = &s->stats_vq_elem;
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VirtIOBalloonStat stat;
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if (!virtqueue_pop(vq, elem)) {
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/* Initialize the stats to get rid of any stale values. This is only
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* needed to handle the case where a guest supports fewer stats than it
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* used to (ie. it has booted into an old kernel).
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while (iov_to_buf(elem->out_sg, elem->out_num, &stat, offset, sizeof(stat))
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uint16_t tag = tswap16(stat.tag);
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uint64_t val = tswap64(stat.val);
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offset += sizeof(stat);
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if (tag < VIRTIO_BALLOON_S_NR)
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s->stats_vq_offset = offset;
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complete_stats_request(s);
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static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
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VirtIOBalloon *dev = to_virtio_balloon(vdev);
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struct virtio_balloon_config config;
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config.num_pages = cpu_to_le32(dev->num_pages);
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config.actual = cpu_to_le32(dev->actual);
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memcpy(config_data, &config, 8);
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static void virtio_balloon_set_config(VirtIODevice *vdev,
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const uint8_t *config_data)
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VirtIOBalloon *dev = to_virtio_balloon(vdev);
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struct virtio_balloon_config config;
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memcpy(&config, config_data, 8);
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dev->actual = le32_to_cpu(config.actual);
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static uint32_t virtio_balloon_get_features(VirtIODevice *vdev, uint32_t f)
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f |= (1 << VIRTIO_BALLOON_F_STATS_VQ);
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static void virtio_balloon_stat(void *opaque, MonitorCompletion cb,
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VirtIOBalloon *dev = opaque;
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/* For now, only allow one request at a time. This restriction can be
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* removed later by queueing callback and data pairs.
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if (dev->stats_callback != NULL) {
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dev->stats_callback = cb;
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dev->stats_opaque_callback_data = cb_data;
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if (ENABLE_GUEST_STATS
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&& (dev->vdev.guest_features & (1 << VIRTIO_BALLOON_F_STATS_VQ))) {
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virtqueue_push(dev->svq, &dev->stats_vq_elem, dev->stats_vq_offset);
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virtio_notify(&dev->vdev, dev->svq);
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/* Stats are not supported. Clear out any stale values that might
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* have been set by a more featureful guest kernel.
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complete_stats_request(dev);
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static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
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VirtIOBalloon *dev = opaque;
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if (target > ram_size) {
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dev->num_pages = (ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
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virtio_notify_config(&dev->vdev);
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static void virtio_balloon_save(QEMUFile *f, void *opaque)
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VirtIOBalloon *s = opaque;
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virtio_save(&s->vdev, f);
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qemu_put_be32(f, s->num_pages);
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qemu_put_be32(f, s->actual);
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static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
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VirtIOBalloon *s = opaque;
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virtio_load(&s->vdev, f);
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s->num_pages = qemu_get_be32(f);
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s->actual = qemu_get_be32(f);
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VirtIODevice *virtio_balloon_init(DeviceState *dev)
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s = (VirtIOBalloon *)virtio_common_init("virtio-balloon",
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8, sizeof(VirtIOBalloon));
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s->vdev.get_config = virtio_balloon_get_config;
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s->vdev.set_config = virtio_balloon_set_config;
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s->vdev.get_features = virtio_balloon_get_features;
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ret = qemu_add_balloon_handler(virtio_balloon_to_target,
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virtio_balloon_stat, s);
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virtio_cleanup(&s->vdev);
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s->ivq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
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s->dvq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
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s->svq = virtio_add_queue(&s->vdev, 128, virtio_balloon_receive_stats);
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register_savevm(dev, "virtio-balloon", -1, 1,
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virtio_balloon_save, virtio_balloon_load, s);
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void virtio_balloon_exit(VirtIODevice *vdev)
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VirtIOBalloon *s = DO_UPCAST(VirtIOBalloon, vdev, vdev);
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unregister_savevm(s->qdev, "virtio-balloon", s);
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virtio_cleanup(vdev);