Re: [PATCH v6 26/36] vfio/migration: Multifd device state transfer support - received buffers queuing

["Cédric Le Goater" <clg@redhat.com>]

On 3/4/25 23:03, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> The multifd received data needs to be reassembled since device state
> packets sent via different multifd channels can arrive out-of-order.
> 
> Therefore, each VFIO device state packet carries a header indicating its
> position in the stream.
> The raw device state data is saved into a VFIOStateBuffer for later
> in-order loading into the device.
> 
> The last such VFIO device state packet should have
> VFIO_DEVICE_STATE_CONFIG_STATE flag set and carry the device config state.
> 
> 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 | 163 ++++++++++++++++++++++++++++++++++++
>   hw/vfio/migration-multifd.h |   3 +
>   hw/vfio/migration.c         |   1 +
>   hw/vfio/trace-events        |   1 +
>   4 files changed, 168 insertions(+)
> 
> diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c
> index 091dc43210ad..79df11b7baa9 100644
> --- a/hw/vfio/migration-multifd.c
> +++ b/hw/vfio/migration-multifd.c
> @@ -32,18 +32,181 @@ typedef struct VFIODeviceStatePacket {
>       uint8_t data[0];
>   } QEMU_PACKED VFIODeviceStatePacket;
>   
> +/* type safety */
> +typedef struct VFIOStateBuffers {
> +    GArray *array;
> +} VFIOStateBuffers;
> +
> +typedef struct VFIOStateBuffer {
> +    bool is_present;
> +    char *data;
> +    size_t len;
> +} VFIOStateBuffer;
> +
>   typedef struct VFIOMultifd {
> +    VFIOStateBuffers load_bufs;
> +    QemuCond load_bufs_buffer_ready_cond;
> +    QemuMutex load_bufs_mutex; /* Lock order: this lock -> BQL */
> +    uint32_t load_buf_idx;
> +    uint32_t load_buf_idx_last;
>   } VFIOMultifd;
>   
> +static void vfio_state_buffer_clear(gpointer data)
> +{
> +    VFIOStateBuffer *lb = data;
> +
> +    if (!lb->is_present) {
> +        return;
> +    }
> +
> +    g_clear_pointer(&lb->data, g_free);
> +    lb->is_present = false;
> +}
> +
> +static void vfio_state_buffers_init(VFIOStateBuffers *bufs)
> +{
> +    bufs->array = g_array_new(FALSE, TRUE, sizeof(VFIOStateBuffer));
> +    g_array_set_clear_func(bufs->array, vfio_state_buffer_clear);
> +}
> +
> +static void vfio_state_buffers_destroy(VFIOStateBuffers *bufs)
> +{
> +    g_clear_pointer(&bufs->array, g_array_unref);
> +}
> +
> +static void vfio_state_buffers_assert_init(VFIOStateBuffers *bufs)
> +{
> +    assert(bufs->array);
> +}
> +
> +static unsigned int vfio_state_buffers_size_get(VFIOStateBuffers *bufs)
> +{
> +    return bufs->array->len;
> +}
> +
> +static void vfio_state_buffers_size_set(VFIOStateBuffers *bufs,
> +                                        unsigned int size)
> +{
> +    g_array_set_size(bufs->array, size);
> +}
> +
> +static VFIOStateBuffer *vfio_state_buffers_at(VFIOStateBuffers *bufs,
> +                                              unsigned int idx)
> +{
> +    return &g_array_index(bufs->array, VFIOStateBuffer, idx);
> +}
> +
> +/* called with load_bufs_mutex locked */
> +static bool vfio_load_state_buffer_insert(VFIODevice *vbasedev,
> +                                          VFIODeviceStatePacket *packet,
> +                                          size_t packet_total_size,
> +                                          Error **errp)
> +{
> +    VFIOMigration *migration = vbasedev->migration;
> +    VFIOMultifd *multifd = migration->multifd;
> +    VFIOStateBuffer *lb;
> +
> +    vfio_state_buffers_assert_init(&multifd->load_bufs);
> +    if (packet->idx >= vfio_state_buffers_size_get(&multifd->load_bufs)) {
> +        vfio_state_buffers_size_set(&multifd->load_bufs, packet->idx + 1);
> +    }
> +
> +    lb = vfio_state_buffers_at(&multifd->load_bufs, packet->idx);
> +    if (lb->is_present) {
> +        error_setg(errp, "%s: state buffer %" PRIu32 " already filled",
> +                   vbasedev->name, packet->idx);
> +        return false;
> +    }
> +
> +    assert(packet->idx >= multifd->load_buf_idx);
> +
> +    lb->data = g_memdup2(&packet->data, packet_total_size - sizeof(*packet));
> +    lb->len = packet_total_size - sizeof(*packet);
> +    lb->is_present = true;
> +
> +    return true;
> +}
> +
> +bool vfio_multifd_load_state_buffer(void *opaque, char *data, size_t data_size,
> +                                    Error **errp)
> +{
> +    VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +    VFIOMultifd *multifd = migration->multifd;
> +    VFIODeviceStatePacket *packet = (VFIODeviceStatePacket *)data;
> +
> +    if (!vfio_multifd_transfer_enabled(vbasedev)) {
> +        error_setg(errp,
> +                   "%s: got device state packet but not doing multifd transfer",
> +                   vbasedev->name);
> +        return false;
> +    }
> +
> +    assert(multifd);
> +
> +    if (data_size < sizeof(*packet)) {
> +        error_setg(errp, "%s: packet too short at %zu (min is %zu)",
> +                   vbasedev->name, data_size, sizeof(*packet));
> +        return false;
> +    }
> +
> +    if (packet->version != VFIO_DEVICE_STATE_PACKET_VER_CURRENT) {
> +        error_setg(errp, "%s: packet has unknown version %" PRIu32,
> +                   vbasedev->name, packet->version);
> +        return false;
> +    }
> +
> +    if (packet->idx == UINT32_MAX) {
> +        error_setg(errp, "%s: packet index is invalid", vbasedev->name);
> +        return false;
> +    }
> +
> +    trace_vfio_load_state_device_buffer_incoming(vbasedev->name, packet->idx);
> +
> +    /*
> +     * Holding BQL here would violate the lock order and can cause
> +     * a deadlock once we attempt to lock load_bufs_mutex below.
> +     */
> +    assert(!bql_locked());
> +
> +    WITH_QEMU_LOCK_GUARD(&multifd->load_bufs_mutex) {
> +        /* config state packet should be the last one in the stream */
> +        if (packet->flags & VFIO_DEVICE_STATE_CONFIG_STATE) {
> +            multifd->load_buf_idx_last = packet->idx;
> +        }
> +
> +        if (!vfio_load_state_buffer_insert(vbasedev, packet, data_size,
> +                                           errp)) {
> +            return false;
> +        }
> +
> +        qemu_cond_signal(&multifd->load_bufs_buffer_ready_cond);
> +    }
> +
> +    return true;
> +}
> +
>   static VFIOMultifd *vfio_multifd_new(void)
>   {
>       VFIOMultifd *multifd = g_new(VFIOMultifd, 1);
>   
> +    vfio_state_buffers_init(&multifd->load_bufs);
> +
> +    qemu_mutex_init(&multifd->load_bufs_mutex);
> +
> +    multifd->load_buf_idx = 0;
> +    multifd->load_buf_idx_last = UINT32_MAX;
> +    qemu_cond_init(&multifd->load_bufs_buffer_ready_cond);
> +
>       return multifd;
>   }
>   
>   static void vfio_multifd_free(VFIOMultifd *multifd)
>   {
> +    vfio_state_buffers_destroy(&multifd->load_bufs);
> +    qemu_cond_destroy(&multifd->load_bufs_buffer_ready_cond);
> +    qemu_mutex_destroy(&multifd->load_bufs_mutex);
> +
>       g_free(multifd);
>   }
>   
> diff --git a/hw/vfio/migration-multifd.h b/hw/vfio/migration-multifd.h
> index 2a7a76164f29..8c6320fcb484 100644
> --- a/hw/vfio/migration-multifd.h
> +++ b/hw/vfio/migration-multifd.h
> @@ -20,4 +20,7 @@ void vfio_multifd_cleanup(VFIODevice *vbasedev);
>   bool vfio_multifd_transfer_supported(void);
>   bool vfio_multifd_transfer_enabled(VFIODevice *vbasedev);
>   
> +bool vfio_multifd_load_state_buffer(void *opaque, char *data, size_t data_size,
> +                                    Error **errp);
> +
>   #endif
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 3c8286ae6230..ecc4ee940567 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -801,6 +801,7 @@ static const SaveVMHandlers savevm_vfio_handlers = {
>       .load_setup = vfio_load_setup,
>       .load_cleanup = vfio_load_cleanup,
>       .load_state = vfio_load_state,
> +    .load_state_buffer = vfio_multifd_load_state_buffer,
>       .switchover_ack_needed = vfio_switchover_ack_needed,
>   };
>   
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index a02c668f28a4..404ea079b25c 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -154,6 +154,7 @@ vfio_load_device_config_state_start(const char *name) " (%s)"
>   vfio_load_device_config_state_end(const char *name) " (%s)"
>   vfio_load_state(const char *name, uint64_t data) " (%s) data 0x%"PRIx64
>   vfio_load_state_device_data(const char *name, uint64_t data_size, int ret) " (%s) size %"PRIu64" ret %d"
> +vfio_load_state_device_buffer_incoming(const char *name, uint32_t idx) " (%s) idx %"PRIu32
>   vfio_migration_realize(const char *name) " (%s)"
>   vfio_migration_set_device_state(const char *name, const char *state) " (%s) state %s"
>   vfio_migration_set_state(const char *name, const char *new_state, const char *recover_state) " (%s) new state %s, recover state %s"
>