Commit 2bbadb08 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Michael S. Tsirkin
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virtio-balloon: fix QEMU 4.0 config size migration incompatibility 



The virtio-balloon config size changed in QEMU 4.0 even for existing
machine types.  Migration from QEMU 3.1 to 4.0 can fail in some
circumstances with the following error:

  qemu-system-x86_64: get_pci_config_device: Bad config data: i=0x10 read: a1 device: 1 cmask: ff wmask: c0 w1cmask:0

This happens because the virtio-balloon config size affects the VIRTIO
Legacy I/O Memory PCI BAR size.

Introduce a qdev property called "qemu-4-0-config-size" and enable it
only for the QEMU 4.0 machine types.  This way <4.0 machine types use
the old size, 4.0 uses the larger size, and >4.0 machine types use the
appropriate size depending on enabled virtio-balloon features.

Live migration to and from old QEMUs to QEMU 4.1 works again as long as
a versioned machine type is specified (do not use just "pc"!).

Originally-by: default avatarWolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20190710141440.27635-1-stefanha@redhat.com>
Reviewed-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: default avatarWolfgang Bumiller <w.bumiller@proxmox.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 4d90b7a0

hw/core/machine.c

+2 −0
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ GlobalProperty hw_compat_4_0[] = { 
    { "virtio-vga",     "edid", "false" },

    { "virtio-gpu-pci", "edid", "false" },

    { "virtio-device", "use-started", "false" },

    { "virtio-balloon-device", "qemu-4-0-config-size", "true" },

};

const size_t hw_compat_4_0_len = G_N_ELEMENTS(hw_compat_4_0);
@@ -49,6 +50,7 @@ GlobalProperty hw_compat_3_1[] = { 
    { "usb-tablet", "serial", "42" },

    { "virtio-blk-device", "discard", "false" },

    { "virtio-blk-device", "write-zeroes", "false" },

    { "virtio-balloon-device", "qemu-4-0-config-size", "false" },

};

const size_t hw_compat_3_1_len = G_N_ELEMENTS(hw_compat_3_1);

hw/virtio/virtio-balloon.c

+25 −3
Original line number Diff line number Diff line
@@ -615,6 +615,22 @@ virtio_balloon_free_page_report_notify(NotifierWithReturn *n, void *data) 
    return 0;

}



static size_t virtio_balloon_config_size(VirtIOBalloon *s)

{

    uint64_t features = s->host_features;



    if (s->qemu_4_0_config_size) {

        return sizeof(struct virtio_balloon_config);

    }

    if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON)) {

        return sizeof(struct virtio_balloon_config);

    }

    if (virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {

        return offsetof(struct virtio_balloon_config, poison_val);

    }

    return offsetof(struct virtio_balloon_config, free_page_report_cmd_id);

}



static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)

{

    VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
@@ -635,7 +651,7 @@ static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data) 
    }



    trace_virtio_balloon_get_config(config.num_pages, config.actual);

    memcpy(config_data, &config, sizeof(struct virtio_balloon_config));

    memcpy(config_data, &config, virtio_balloon_config_size(dev));

}



static int build_dimm_list(Object *obj, void *opaque)
@@ -679,7 +695,7 @@ static void virtio_balloon_set_config(VirtIODevice *vdev, 
    uint32_t oldactual = dev->actual;

    ram_addr_t vm_ram_size = get_current_ram_size();



    memcpy(&config, config_data, sizeof(struct virtio_balloon_config));

    memcpy(&config, config_data, virtio_balloon_config_size(dev));

    dev->actual = le32_to_cpu(config.actual);

    if (dev->actual != oldactual) {

        qapi_event_send_balloon_change(vm_ram_size -
@@ -766,7 +782,7 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) 
    int ret;



    virtio_init(vdev, "virtio-balloon", VIRTIO_ID_BALLOON,

                sizeof(struct virtio_balloon_config));

                virtio_balloon_config_size(s));



    ret = qemu_add_balloon_handler(virtio_balloon_to_target,

                                   virtio_balloon_stat, s);
@@ -897,6 +913,12 @@ static Property virtio_balloon_properties[] = { 
                    VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),

    DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features,

                    VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),

    /* QEMU 4.0 accidentally changed the config size even when free-page-hint

     * is disabled, resulting in QEMU 3.1 migration incompatibility.  This

     * property retains this quirk for QEMU 4.1 machine types.

     */

    DEFINE_PROP_BOOL("qemu-4-0-config-size", VirtIOBalloon,

                     qemu_4_0_config_size, false),

    DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD,

                     IOThread *),

    DEFINE_PROP_END_OF_LIST(),

include/hw/virtio/virtio-balloon.h

+2 −0
Original line number Diff line number Diff line
@@ -71,6 +71,8 @@ typedef struct VirtIOBalloon { 
    int64_t stats_poll_interval;

    uint32_t host_features;

    PartiallyBalloonedPage *pbp;



    bool qemu_4_0_config_size;

} VirtIOBalloon;



#endif