* David Hildenbrand ([email protected]) wrote: > The bitmap and the size are immutable while migration is active: see > virtio_mem_is_busy(). We can migrate this information early, before > migrating any actual RAM content. Further, all information we need for > sanity checks is immutable as well. > > Having this information in place early will, for example, allow for > properly preallocating memory before touching these memory locations > during RAM migration: this way, we can make sure that all memory was > actually preallocated and that any user errors (e.g., insufficient > hugetlb pages) can be handled gracefully. > > In contrast, usable_region_size and requested_size can theoretically > still be modified on the source while the VM is running. Keep migrating > these properties the usual, late, way. > > Use a new device property to keep behavior of compat machines > unmodified.
Can you get me a migration file from this? I want to try and understand what happens when you have the vmstate_register together with the ->vmsd - I'm not quite sure what ends up in the output. Preferably for a VM with two virtio-mem's. Dave > Signed-off-by: David Hildenbrand <[email protected]> > --- > hw/core/machine.c | 4 ++- > hw/virtio/virtio-mem.c | 51 ++++++++++++++++++++++++++++++++-- > include/hw/virtio/virtio-mem.h | 8 ++++++ > 3 files changed, 60 insertions(+), 3 deletions(-) > > diff --git a/hw/core/machine.c b/hw/core/machine.c > index 616f3a207c..29b57f6448 100644 > --- a/hw/core/machine.c > +++ b/hw/core/machine.c > @@ -41,7 +41,9 @@ > #include "hw/virtio/virtio-pci.h" > #include "qom/object_interfaces.h" > > -GlobalProperty hw_compat_7_2[] = {}; > +GlobalProperty hw_compat_7_2[] = { > + { "virtio-mem", "x-early-migration", "false" }, > +}; > const size_t hw_compat_7_2_len = G_N_ELEMENTS(hw_compat_7_2); > > GlobalProperty hw_compat_7_1[] = { > diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c > index 02f7b5469a..51666baa01 100644 > --- a/hw/virtio/virtio-mem.c > +++ b/hw/virtio/virtio-mem.c > @@ -31,6 +31,8 @@ > #include CONFIG_DEVICES > #include "trace.h" > > +static const VMStateDescription vmstate_virtio_mem_device_early; > + > /* > * We only had legacy x86 guests that did not support > * VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE. Other targets don't have legacy > guests. > @@ -878,6 +880,10 @@ static void virtio_mem_device_realize(DeviceState *dev, > Error **errp) > > host_memory_backend_set_mapped(vmem->memdev, true); > vmstate_register_ram(&vmem->memdev->mr, DEVICE(vmem)); > + if (vmem->early_migration) { > + vmstate_register(VMSTATE_IF(vmem), VMSTATE_INSTANCE_ID_ANY, > + &vmstate_virtio_mem_device_early, vmem); > + } > qemu_register_reset(virtio_mem_system_reset, vmem); > > /* > @@ -899,6 +905,10 @@ static void virtio_mem_device_unrealize(DeviceState *dev) > */ > memory_region_set_ram_discard_manager(&vmem->memdev->mr, NULL); > qemu_unregister_reset(virtio_mem_system_reset, vmem); > + if (vmem->early_migration) { > + vmstate_unregister(VMSTATE_IF(vmem), > &vmstate_virtio_mem_device_early, > + vmem); > + } > vmstate_unregister_ram(&vmem->memdev->mr, DEVICE(vmem)); > host_memory_backend_set_mapped(vmem->memdev, false); > virtio_del_queue(vdev, 0); > @@ -1015,18 +1025,53 @@ static const VMStateDescription > vmstate_virtio_mem_sanity_checks = { > }, > }; > > +static bool virtio_mem_vmstate_field_exists(void *opaque, int version_id) > +{ > + const VirtIOMEM *vmem = VIRTIO_MEM(opaque); > + > + /* With early migration, these fields were already migrated. */ > + return !vmem->early_migration; > +} > + > static const VMStateDescription vmstate_virtio_mem_device = { > .name = "virtio-mem-device", > .minimum_version_id = 1, > .version_id = 1, > .priority = MIG_PRI_VIRTIO_MEM, > .post_load = virtio_mem_post_load, > + .fields = (VMStateField[]) { > + VMSTATE_WITH_TMP_TEST(VirtIOMEM, virtio_mem_vmstate_field_exists, > + VirtIOMEMMigSanityChecks, > + vmstate_virtio_mem_sanity_checks), > + VMSTATE_UINT64(usable_region_size, VirtIOMEM), > + VMSTATE_UINT64_TEST(size, VirtIOMEM, > virtio_mem_vmstate_field_exists), > + VMSTATE_UINT64(requested_size, VirtIOMEM), > + VMSTATE_BITMAP_TEST(bitmap, VirtIOMEM, > virtio_mem_vmstate_field_exists, > + 0, bitmap_size), > + VMSTATE_END_OF_LIST() > + }, > +}; > + > +/* > + * Transfer properties that are immutable while migration is active early, > + * such that we have have this information around before migrating any RAM > + * content. > + * > + * Note that virtio_mem_is_busy() makes sure these properties can no longer > + * change on the migration source until migration completed. > + * > + * With QEMU compat machines, we transmit these properties later, via > + * vmstate_virtio_mem_device instead -- see > virtio_mem_vmstate_field_exists(). > + */ > +static const VMStateDescription vmstate_virtio_mem_device_early = { > + .name = "virtio-mem-device-early", > + .minimum_version_id = 1, > + .version_id = 1, > + .immutable = 1, > .fields = (VMStateField[]) { > VMSTATE_WITH_TMP(VirtIOMEM, VirtIOMEMMigSanityChecks, > vmstate_virtio_mem_sanity_checks), > - VMSTATE_UINT64(usable_region_size, VirtIOMEM), > VMSTATE_UINT64(size, VirtIOMEM), > - VMSTATE_UINT64(requested_size, VirtIOMEM), > VMSTATE_BITMAP(bitmap, VirtIOMEM, 0, bitmap_size), > VMSTATE_END_OF_LIST() > }, > @@ -1211,6 +1256,8 @@ static Property virtio_mem_properties[] = { > DEFINE_PROP_ON_OFF_AUTO(VIRTIO_MEM_UNPLUGGED_INACCESSIBLE_PROP, > VirtIOMEM, > unplugged_inaccessible, ON_OFF_AUTO_AUTO), > #endif > + DEFINE_PROP_BOOL(VIRTIO_MEM_EARLY_MIGRATION_PROP, VirtIOMEM, > + early_migration, true), > DEFINE_PROP_END_OF_LIST(), > }; > > diff --git a/include/hw/virtio/virtio-mem.h b/include/hw/virtio/virtio-mem.h > index 7745cfc1a3..f15e561785 100644 > --- a/include/hw/virtio/virtio-mem.h > +++ b/include/hw/virtio/virtio-mem.h > @@ -31,6 +31,7 @@ OBJECT_DECLARE_TYPE(VirtIOMEM, VirtIOMEMClass, > #define VIRTIO_MEM_BLOCK_SIZE_PROP "block-size" > #define VIRTIO_MEM_ADDR_PROP "memaddr" > #define VIRTIO_MEM_UNPLUGGED_INACCESSIBLE_PROP "unplugged-inaccessible" > +#define VIRTIO_MEM_EARLY_MIGRATION_PROP "x-early-migration" > #define VIRTIO_MEM_PREALLOC_PROP "prealloc" > > struct VirtIOMEM { > @@ -74,6 +75,13 @@ struct VirtIOMEM { > /* whether to prealloc memory when plugging new blocks */ > bool prealloc; > > + /* > + * Whether we migrate properties that are immutable while migration is > + * active early, before state of other devices and especially, before > + * migrating any RAM content. > + */ > + bool early_migration; > + > /* notifiers to notify when "size" changes */ > NotifierList size_change_notifiers; > > -- > 2.39.0 > -- Dr. David Alan Gilbert / [email protected] / Manchester, UK
