Re: [PATCH v6 30/36] vfio/migration: Multifd device state transfer support - send side

["Cédric Le Goater" <clg@redhat.com>]

On 3/4/25 23:03, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> Implement the multifd device state transfer via additional per-device
> thread inside save_live_complete_precopy_thread handler.
> 
> Switch between doing the data transfer in the new handler and doing it
> in the old save_state handler depending if VFIO multifd transfer is enabled
> or not.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.


> ---
>   hw/vfio/migration-multifd.c   | 142 ++++++++++++++++++++++++++++++++++
>   hw/vfio/migration-multifd.h   |   6 ++
>   hw/vfio/migration.c           |  22 ++++--
>   hw/vfio/trace-events          |   2 +
>   include/hw/vfio/vfio-common.h |   6 ++
>   5 files changed, 172 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c
> index 1d81233c755f..bfb9a72fa450 100644
> --- a/hw/vfio/migration-multifd.c
> +++ b/hw/vfio/migration-multifd.c
> @@ -496,6 +496,148 @@ bool vfio_multifd_setup(VFIODevice *vbasedev, bool alloc_multifd, Error **errp)
>       return true;
>   }
>   
> +void vfio_multifd_emit_dummy_eos(VFIODevice *vbasedev, QEMUFile *f)
> +{
> +    assert(vfio_multifd_transfer_enabled(vbasedev));
> +
> +    /*
> +     * Emit dummy NOP data on the main migration channel since the actual
> +     * device state transfer is done via multifd channels.
> +     */
> +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> +}
> +
> +static bool
> +vfio_save_complete_precopy_thread_config_state(VFIODevice *vbasedev,
> +                                               char *idstr,
> +                                               uint32_t instance_id,
> +                                               uint32_t idx,
> +                                               Error **errp)
> +{
> +    g_autoptr(QIOChannelBuffer) bioc = NULL;
> +    g_autoptr(QEMUFile) f = NULL;
> +    int ret;
> +    g_autofree VFIODeviceStatePacket *packet = NULL;
> +    size_t packet_len;
> +
> +    bioc = qio_channel_buffer_new(0);
> +    qio_channel_set_name(QIO_CHANNEL(bioc), "vfio-device-config-save");
> +
> +    f = qemu_file_new_output(QIO_CHANNEL(bioc));
> +
> +    if (vfio_save_device_config_state(f, vbasedev, errp)) {
> +        return false;
> +    }
> +
> +    ret = qemu_fflush(f);
> +    if (ret) {
> +        error_setg(errp, "%s: save config state flush failed: %d",
> +                   vbasedev->name, ret);
> +        return false;
> +    }
> +
> +    packet_len = sizeof(*packet) + bioc->usage;
> +    packet = g_malloc0(packet_len);
> +    packet->version = VFIO_DEVICE_STATE_PACKET_VER_CURRENT;
> +    packet->idx = idx;
> +    packet->flags = VFIO_DEVICE_STATE_CONFIG_STATE;
> +    memcpy(&packet->data, bioc->data, bioc->usage);
> +
> +    if (!multifd_queue_device_state(idstr, instance_id,
> +                                    (char *)packet, packet_len)) {
> +        error_setg(errp, "%s: multifd config data queuing failed",
> +                   vbasedev->name);
> +        return false;
> +    }
> +
> +    vfio_mig_add_bytes_transferred(packet_len);
> +
> +    return true;
> +}
> +
> +/*
> + * This thread is spawned by the migration core directly via
> + * .save_live_complete_precopy_thread SaveVMHandler.
> + *
> + * It exits after either:
> + * * completing saving the remaining device state and device config, OR:
> + * * encountering some error while doing the above, OR:
> + * * being forcefully aborted by the migration core by
> + *   multifd_device_state_save_thread_should_exit() returning true.
> + */
> +bool
> +vfio_multifd_save_complete_precopy_thread(SaveLiveCompletePrecopyThreadData *d,
> +                                          Error **errp)
> +{
> +    VFIODevice *vbasedev = d->handler_opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +    bool ret = false;
> +    g_autofree VFIODeviceStatePacket *packet = NULL;
> +    uint32_t idx;
> +
> +    if (!vfio_multifd_transfer_enabled(vbasedev)) {
> +        /* Nothing to do, vfio_save_complete_precopy() does the transfer. */
> +        return true;
> +    }
> +
> +    trace_vfio_save_complete_precopy_thread_start(vbasedev->name,
> +                                                  d->idstr, d->instance_id);
> +
> +    /* We reach here with device state STOP or STOP_COPY only */
> +    if (vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
> +                                 VFIO_DEVICE_STATE_STOP, errp)) {
> +        goto thread_exit;
> +    }
> +
> +    packet = g_malloc0(sizeof(*packet) + migration->data_buffer_size);
> +    packet->version = VFIO_DEVICE_STATE_PACKET_VER_CURRENT;
> +
> +    for (idx = 0; ; idx++) {
> +        ssize_t data_size;
> +        size_t packet_size;
> +
> +        if (multifd_device_state_save_thread_should_exit()) {
> +            error_setg(errp, "operation cancelled");
> +            goto thread_exit;
> +        }
> +
> +        data_size = read(migration->data_fd, &packet->data,
> +                         migration->data_buffer_size);
> +        if (data_size < 0) {
> +            error_setg(errp, "%s: reading state buffer %" PRIu32 " failed: %d",
> +                       vbasedev->name, idx, errno);
> +            goto thread_exit;
> +        } else if (data_size == 0) {
> +            break;
> +        }
> +
> +        packet->idx = idx;
> +        packet_size = sizeof(*packet) + data_size;
> +
> +        if (!multifd_queue_device_state(d->idstr, d->instance_id,
> +                                        (char *)packet, packet_size)) {
> +            error_setg(errp, "%s: multifd data queuing failed", vbasedev->name);
> +            goto thread_exit;
> +        }
> +
> +        vfio_mig_add_bytes_transferred(packet_size);
> +    }
> +
> +    if (!vfio_save_complete_precopy_thread_config_state(vbasedev,
> +                                                        d->idstr,
> +                                                        d->instance_id,
> +                                                        idx, errp)) {
> +        goto thread_exit;
> +   }
> +
> +    ret = true;
> +
> +thread_exit:
> +    trace_vfio_save_complete_precopy_thread_end(vbasedev->name, ret);
> +
> +    return ret;
> +}
> +
>   int vfio_multifd_switchover_start(VFIODevice *vbasedev)
>   {
>       VFIOMigration *migration = vbasedev->migration;
> diff --git a/hw/vfio/migration-multifd.h b/hw/vfio/migration-multifd.h
> index f0d28fcef2ea..a664051eb8ae 100644
> --- a/hw/vfio/migration-multifd.h
> +++ b/hw/vfio/migration-multifd.h
> @@ -23,6 +23,12 @@ bool vfio_multifd_transfer_enabled(VFIODevice *vbasedev);
>   bool vfio_multifd_load_state_buffer(void *opaque, char *data, size_t data_size,
>                                       Error **errp);
>   
> +void vfio_multifd_emit_dummy_eos(VFIODevice *vbasedev, QEMUFile *f);
> +
> +bool
> +vfio_multifd_save_complete_precopy_thread(SaveLiveCompletePrecopyThreadData *d,
> +                                          Error **errp);
> +
>   int vfio_multifd_switchover_start(VFIODevice *vbasedev);
>   
>   #endif
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index f325a619c3ed..24bdc9e24c71 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -120,10 +120,10 @@ static void vfio_migration_set_device_state(VFIODevice *vbasedev,
>       vfio_migration_send_event(vbasedev);
>   }
>   
> -static int vfio_migration_set_state(VFIODevice *vbasedev,
> -                                    enum vfio_device_mig_state new_state,
> -                                    enum vfio_device_mig_state recover_state,
> -                                    Error **errp)
> +int vfio_migration_set_state(VFIODevice *vbasedev,
> +                             enum vfio_device_mig_state new_state,
> +                             enum vfio_device_mig_state recover_state,
> +                             Error **errp)
>   {
>       VFIOMigration *migration = vbasedev->migration;
>       uint64_t buf[DIV_ROUND_UP(sizeof(struct vfio_device_feature) +
> @@ -238,8 +238,7 @@ static int vfio_load_buffer(QEMUFile *f, VFIODevice *vbasedev,
>       return ret;
>   }
>   
> -static int vfio_save_device_config_state(QEMUFile *f, void *opaque,
> -                                         Error **errp)
> +int vfio_save_device_config_state(QEMUFile *f, void *opaque, Error **errp)
>   {
>       VFIODevice *vbasedev = opaque;
>       int ret;
> @@ -638,6 +637,11 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
>       int ret;
>       Error *local_err = NULL;
>   
> +    if (vfio_multifd_transfer_enabled(vbasedev)) {
> +        vfio_multifd_emit_dummy_eos(vbasedev, f);
> +        return 0;
> +    }
> +
>       trace_vfio_save_complete_precopy_start(vbasedev->name);
>   
>       /* We reach here with device state STOP or STOP_COPY only */
> @@ -669,6 +673,11 @@ static void vfio_save_state(QEMUFile *f, void *opaque)
>       Error *local_err = NULL;
>       int ret;
>   
> +    if (vfio_multifd_transfer_enabled(vbasedev)) {
> +        vfio_multifd_emit_dummy_eos(vbasedev, f);
> +        return;
> +    }
> +
>       ret = vfio_save_device_config_state(f, opaque, &local_err);
>       if (ret) {
>           error_prepend(&local_err,
> @@ -815,6 +824,7 @@ static const SaveVMHandlers savevm_vfio_handlers = {
>       .is_active_iterate = vfio_is_active_iterate,
>       .save_live_iterate = vfio_save_iterate,
>       .save_live_complete_precopy = vfio_save_complete_precopy,
> +    .save_live_complete_precopy_thread = vfio_multifd_save_complete_precopy_thread,
>       .save_state = vfio_save_state,
>       .load_setup = vfio_load_setup,
>       .load_cleanup = vfio_load_cleanup,
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index d6b7e34faa39..9347e3a5f660 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -171,6 +171,8 @@ vfio_save_block_precopy_empty_hit(const char *name) " (%s)"
>   vfio_save_cleanup(const char *name) " (%s)"
>   vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d"
>   vfio_save_complete_precopy_start(const char *name) " (%s)"
> +vfio_save_complete_precopy_thread_start(const char *name, const char *idstr, uint32_t instance_id) " (%s) idstr %s instance %"PRIu32
> +vfio_save_complete_precopy_thread_end(const char *name, int ret) " (%s) ret %d"
>   vfio_save_device_config_state(const char *name) " (%s)"
>   vfio_save_iterate(const char *name, uint64_t precopy_init_size, uint64_t precopy_dirty_size) " (%s) precopy initial size %"PRIu64" precopy dirty size %"PRIu64
>   vfio_save_iterate_start(const char *name) " (%s)"
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 9d72ac1eae8a..961931d9f457 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -298,6 +298,7 @@ void vfio_mig_add_bytes_transferred(unsigned long val);
>   bool vfio_device_state_is_running(VFIODevice *vbasedev);
>   bool vfio_device_state_is_precopy(VFIODevice *vbasedev);
>   
> +int vfio_save_device_config_state(QEMUFile *f, void *opaque, Error **errp);
>   int vfio_load_device_config_state(QEMUFile *f, void *opaque);
>   
>   #ifdef CONFIG_LINUX
> @@ -314,6 +315,11 @@ struct vfio_info_cap_header *
>   vfio_get_device_info_cap(struct vfio_device_info *info, uint16_t id);
>   struct vfio_info_cap_header *
>   vfio_get_cap(void *ptr, uint32_t cap_offset, uint16_t id);
> +
> +int vfio_migration_set_state(VFIODevice *vbasedev,
> +                             enum vfio_device_mig_state new_state,
> +                             enum vfio_device_mig_state recover_state,
> +                             Error **errp);
>   #endif
>   
>   bool vfio_migration_realize(VFIODevice *vbasedev, Error **errp);
>