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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: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20190710141440.27635-1-stefanha@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2019-07-10 16:14:40 +02:00 committed by Michael S. Tsirkin
parent 4d90b7a0e4
commit 2bbadb08ce
3 changed files with 29 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
hw/core/machine.c
View File

@ -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);

28
hw/virtio/virtio-balloon.c
View File

@ -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(),

2
include/hw/virtio/virtio-balloon.h
View File

@ -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