| Message ID | 20190710141440.27635-1-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | virtio-balloon: fix QEMU 4.0 config size migration incompatibility | expand |
* 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
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
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(),
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(-)