include/hw/virtio/virtio-balloon.h | 2 ++ hw/core/machine.c | 2 ++ hw/virtio/virtio-balloon.c | 28 +++++++++++++++++++++++++--- 3 files changed, 29 insertions(+), 3 deletions(-)
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>
---
include/hw/virtio/virtio-balloon.h | 2 ++
hw/core/machine.c | 2 ++
hw/virtio/virtio-balloon.c | 28 +++++++++++++++++++++++++---
3 files changed, 29 insertions(+), 3 deletions(-)
diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
index 1afafb12f6..5a99293a45 100644
--- a/include/hw/virtio/virtio-balloon.h
+++ b/include/hw/virtio/virtio-balloon.h
@@ -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
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 2be19ec0cd..c4ead16010 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -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);
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 11fad86d64..e85d1c0d5c 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -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(),
--
2.21.0
On Wed, Jul 10, 2019 at 04:14:40PM +0200, Stefan Hajnoczi wrote:
> 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>
Tested-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Works with my otherwise failing VM from 3.0.1 -> patched-4.0.
Somehow I missed the `DEFINE_PROP_*` macros, sorry, and thanks for
fixing this up.
> ---
> include/hw/virtio/virtio-balloon.h | 2 ++
> hw/core/machine.c | 2 ++
> hw/virtio/virtio-balloon.c | 28 +++++++++++++++++++++++++---
> 3 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> index 1afafb12f6..5a99293a45 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -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
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 2be19ec0cd..c4ead16010 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -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);
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 11fad86d64..e85d1c0d5c 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -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(),
> --
> 2.21.0
>
>
* Wolfgang Bumiller (w.bumiller@proxmox.com) wrote:
> On Wed, Jul 10, 2019 at 04:14:40PM +0200, Stefan Hajnoczi wrote:
> > 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>
>
> Tested-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
>
> Works with my otherwise failing VM from 3.0.1 -> patched-4.0.
> Somehow I missed the `DEFINE_PROP_*` macros, sorry, and thanks for
> fixing this up.
Thanks again for spotting it!
Dave
> > ---
> > include/hw/virtio/virtio-balloon.h | 2 ++
> > hw/core/machine.c | 2 ++
> > hw/virtio/virtio-balloon.c | 28 +++++++++++++++++++++++++---
> > 3 files changed, 29 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> > index 1afafb12f6..5a99293a45 100644
> > --- a/include/hw/virtio/virtio-balloon.h
> > +++ b/include/hw/virtio/virtio-balloon.h
> > @@ -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
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index 2be19ec0cd..c4ead16010 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -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);
> >
> > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> > index 11fad86d64..e85d1c0d5c 100644
> > --- a/hw/virtio/virtio-balloon.c
> > +++ b/hw/virtio/virtio-balloon.c
> > @@ -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(),
> > --
> > 2.21.0
> >
> >
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> 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>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tried 3.1->head and back
Tried head<->head (default options)
in both cases I tried ballooning the guest up and down
Dave
> ---
> include/hw/virtio/virtio-balloon.h | 2 ++
> hw/core/machine.c | 2 ++
> hw/virtio/virtio-balloon.c | 28 +++++++++++++++++++++++++---
> 3 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> index 1afafb12f6..5a99293a45 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -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
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 2be19ec0cd..c4ead16010 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -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);
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 11fad86d64..e85d1c0d5c 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -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(),
> --
> 2.21.0
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
© 2016 - 2026 Red Hat, Inc.