system/ulib/machina/balloon.cpp

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <machina/balloon.h>

#include <fbl/auto_lock.h>
#include <virtio/virtio_ids.h>
#include <zircon/syscalls.h>

static zx_status_t decommit_pages(zx_handle_t vmo, uint64_t addr, uint64_t len) {
    return zx_vmo_op_range(vmo, ZX_VMO_OP_DECOMMIT, addr, len, nullptr, 0);
}

static zx_status_t commit_pages(zx_handle_t vmo, uint64_t addr, uint64_t len) {
    return zx_vmo_op_range(vmo, ZX_VMO_OP_COMMIT, addr, len, nullptr, 0);
}

/* Structure passed to the inflate/deflate queue handler. */
typedef struct queue_ctx {
    // Operation to perform on the queue (inflate or deflate).
    zx_status_t (*op)(zx_handle_t vmo, uint64_t addr, uint64_t len);
    // The VMO to invoke |op| on.
    zx_handle_t vmo;
} queue_ctx_t;

/* Handle balloon inflate/deflate requests.
 *
 * From VIRTIO 1.0 Section 5.5.6:
 *
 * To supply memory to the balloon (aka. inflate):
 *  (a) The driver constructs an array of addresses of unused memory pages.
 *      These addresses are divided by 4096 and the descriptor describing the
 *      resulting 32-bit array is added to the inflateq.
 *
 * To remove memory from the balloon (aka. deflate):
 *  (a) The driver constructs an array of addresses of memory pages it has
 *      previously given to the balloon, as described above. This descriptor is
 *      added to the deflateq.
 *  (b) If the VIRTIO_BALLOON_F_MUST_TELL_HOST feature is negotiated, the guest
 *      informs the device of pages before it uses them.
 *  (c) Otherwise, the guest is allowed to re-use pages previously given to the
 *      balloon before the device has acknowledged their withdrawal.
 */
static zx_status_t queue_range_op(void* addr, uint32_t len, uint16_t flags, uint32_t* used,
                                  void* ctx) {
    queue_ctx_t* balloon_op_ctx = static_cast<queue_ctx_t*>(ctx);
    uint32_t* pfns = static_cast<uint32_t*>(addr);
    uint32_t pfn_count = len / 4;

    // If the driver writes contiguous PFNs to the array we'll batch them up
    // when invoking the inflate/deflate operation.
    uint64_t region_base = 0;
    uint64_t region_length = 0;
    for (uint32_t i = 0; i < pfn_count; ++i) {
        // If we have a contiguous page, increment the length & continue.
        if (region_length > 0 && (region_base + region_length) == pfns[i]) {
            region_length++;
            continue;
        }

        // If we have an existing region; invoke the inflate/deflate op.
        if (region_length > 0) {
            zx_status_t status = balloon_op_ctx->op(balloon_op_ctx->vmo,
                                                    region_base * VirtioBalloon::kPageSize,
                                                    region_length * VirtioBalloon::kPageSize);
            if (status != ZX_OK)
                return status;
        }

        // Create a new region.
        region_base = pfns[i];
        region_length = 1;
    }

    // Handle the last region.
    if (region_length > 0) {
        zx_status_t status = balloon_op_ctx->op(balloon_op_ctx->vmo,
                                                region_base * VirtioBalloon::kPageSize,
                                                region_length * VirtioBalloon::kPageSize);
        if (status != ZX_OK)
            return status;
    }

    return ZX_OK;
}

zx_status_t VirtioBalloon::HandleDescriptor(uint16_t queue_sel) {
    queue_ctx_t ctx;
    switch (queue_sel) {
    case VIRTIO_BALLOON_Q_STATSQ:
        return ZX_OK;
    case VIRTIO_BALLOON_Q_INFLATEQ:
        ctx.op = &decommit_pages;
        break;
    case VIRTIO_BALLOON_Q_DEFLATEQ:
        if (deflate_on_demand_)
            return ZX_OK;
        ctx.op = &commit_pages;
        break;
    default:
        return ZX_ERR_INVALID_ARGS;
    }
    ctx.vmo = vmo_;
    return virtio_queue_handler(&queues_[queue_sel], &queue_range_op, &ctx);
}

zx_status_t VirtioBalloon::HandleQueueNotify(uint16_t queue_sel) {
    zx_status_t status;
    do {
        status = HandleDescriptor(queue_sel);
    } while (status == ZX_ERR_NEXT);
    return status;
}

VirtioBalloon::VirtioBalloon(uintptr_t guest_physmem_addr, size_t guest_physmem_size,
                             zx_handle_t guest_physmem_vmo)
    : VirtioDevice(VIRTIO_ID_BALLOON, &config_, sizeof(config_), queues_, VIRTIO_BALLOON_Q_COUNT,
                   guest_physmem_addr, guest_physmem_size),
      vmo_(guest_physmem_vmo) {
    add_device_features(VIRTIO_BALLOON_F_STATS_VQ | VIRTIO_BALLOON_F_DEFLATE_ON_OOM);
}

void VirtioBalloon::WaitForStatsBuffer(virtio_queue_t* stats_queue) {
    if (!stats_.has_buffer) {
        virtio_queue_wait(stats_queue, &stats_.desc_index);
        stats_.has_buffer = true;
    }
}

zx_status_t VirtioBalloon::RequestStats(StatsHandler handler) {
    virtio_queue_t* stats_queue = &queues_[VIRTIO_BALLOON_Q_STATSQ];

    // stats.mutex needs to be held during the entire time the guest is
    // processing the buffer since we need to make sure no other threads
    // can grab the returned stats buffer before we process it.
    fbl::AutoLock lock(&stats_.mutex);

    // We need an initial buffer we can return to return to the device to
    // request stats from the device. This should be immediately available in
    // the common case but we can race the driver for the initial buffer.
    WaitForStatsBuffer(stats_queue);

    // We have a buffer. We need to return it to the driver. It'll populate
    // a new buffer with stats and then send it back to us.
    stats_.has_buffer = false;
    virtio_queue_return(stats_queue, stats_.desc_index, 0);
    zx_status_t status = NotifyGuest();
    if (status != ZX_OK)
        return status;
    WaitForStatsBuffer(stats_queue);

    virtio_desc_t desc;
    status = virtio_queue_read_desc(stats_queue, stats_.desc_index, &desc);
    if (status != ZX_OK)
        return status;

    if ((desc.len % sizeof(virtio_balloon_stat_t)) != 0)
        return ZX_ERR_IO_DATA_INTEGRITY;

    // Invoke the handler on the stats.
    auto stats = static_cast<const virtio_balloon_stat_t*>(desc.addr);
    size_t stats_count = desc.len / sizeof(virtio_balloon_stat_t);
    handler(stats, stats_count);

    // Note we deliberately do not return the buffer here. This will be done to
    // initiate the next stats request.
    return ZX_OK;
}

zx_status_t VirtioBalloon::UpdateNumPages(uint32_t num_pages) {
    fbl::AutoLock lock(&config_mutex_);
    config_.num_pages = num_pages;

    // Send a config change interrupt to the guest.
    add_isr_flags(VirtioDevice::VIRTIO_ISR_DEVICE);
    return NotifyGuest();
}

uint32_t VirtioBalloon::num_pages() {
    fbl::AutoLock lock(&config_mutex_);
    return config_.num_pages;
}