Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Yan Zhao (yan.y.zhao@intel.com) wrote:
> On Fri, Jun 21, 2019 at 08:31:53AM +0800, Yan Zhao wrote:
> > On Thu, Jun 20, 2019 at 10:37:36PM +0800, Kirti Wankhede wrote:
> > > Added .save_live_pending, .save_live_iterate and .save_live_complete_precopy
> > > functions. These functions handles pre-copy and stop-and-copy phase.
> > > 
> > > In _SAVING|_RUNNING device state or pre-copy phase:
> > > - read pending_bytes
> > > - read data_offset - indicates kernel driver to write data to staging
> > >   buffer which is mmapped.
> > > - read data_size - amount of data in bytes written by vendor driver in migration
> > >   region.
> > > - if data section is trapped, pread() number of bytes in data_size, from
> > >   data_offset.
> > > - if data section is mmaped, read mmaped buffer of size data_size.
> > > - Write data packet to file stream as below:
> > > {VFIO_MIG_FLAG_DEV_DATA_STATE, data_size, actual data,
> > > VFIO_MIG_FLAG_END_OF_STATE }
> > > 
> > > In _SAVING device state or stop-and-copy phase
> > > a. read config space of device and save to migration file stream. This
> > >    doesn't need to be from vendor driver. Any other special config state
> > >    from driver can be saved as data in following iteration.
> > > b. read pending_bytes - indicates kernel driver to write data to staging
> > >    buffer which is mmapped.
> > > c. read data_size - amount of data in bytes written by vendor driver in
> > >    migration region.
> > > d. if data section is trapped, pread() from data_offset of size data_size.
> > > e. if data section is mmaped, read mmaped buffer of size data_size.
> > > f. Write data packet as below:
> > >    {VFIO_MIG_FLAG_DEV_DATA_STATE, data_size, actual data}
> > > g. iterate through steps b to f until (pending_bytes > 0)
> > > h. Write {VFIO_MIG_FLAG_END_OF_STATE}
> > > 
> > > .save_live_iterate runs outside the iothread lock in the migration case, which
> > > could race with asynchronous call to get dirty page list causing data corruption
> > > in mapped migration region. Mutex added here to serial migration buffer read
> > > operation.
> > > 
> > > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > > Reviewed-by: Neo Jia <cjia@nvidia.com>
> > > ---
> > >  hw/vfio/migration.c | 212 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 212 insertions(+)
> > > 
> > > diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> > > index fe0887c27664..0a2f30872316 100644
> > > --- a/hw/vfio/migration.c
> > > +++ b/hw/vfio/migration.c
> > > @@ -107,6 +107,111 @@ static int vfio_migration_set_state(VFIODevice *vbasedev, uint32_t state)
> > >      return 0;
> > >  }
> > >  
> > > +static int vfio_save_buffer(QEMUFile *f, VFIODevice *vbasedev)
> > > +{
> > > +    VFIOMigration *migration = vbasedev->migration;
> > > +    VFIORegion *region = &migration->region.buffer;
> > > +    uint64_t data_offset = 0, data_size = 0;
> > > +    int ret;
> > > +
> > > +    ret = pread(vbasedev->fd, &data_offset, sizeof(data_offset),
> > > +                region->fd_offset + offsetof(struct vfio_device_migration_info,
> > > +                                             data_offset));
> > > +    if (ret != sizeof(data_offset)) {
> > > +        error_report("Failed to get migration buffer data offset %d",
> > > +                     ret);
> > > +        return -EINVAL;
> > > +    }
> > > +
> > > +    ret = pread(vbasedev->fd, &data_size, sizeof(data_size),
> > > +                region->fd_offset + offsetof(struct vfio_device_migration_info,
> > > +                                             data_size));
> > > +    if (ret != sizeof(data_size)) {
> > > +        error_report("Failed to get migration buffer data size %d",
> > > +                     ret);
> > > +        return -EINVAL;
> > > +    }
> > > +
> > how big is the data_size ? 
> > if this size is too big, it may take too much time and block others.
> > 
> > > +    if (data_size > 0) {
> > > +        void *buf = NULL;
> > > +        bool buffer_mmaped = false;
> > > +
> > > +        if (region->mmaps) {
> > > +            int i;
> > > +
> > > +            for (i = 0; i < region->nr_mmaps; i++) {
> > > +                if ((data_offset >= region->mmaps[i].offset) &&
> > > +                    (data_offset < region->mmaps[i].offset +
> > > +                                   region->mmaps[i].size)) {
> > > +                    buf = region->mmaps[i].mmap + (data_offset -
> > > +                                                   region->mmaps[i].offset);
> > > +                    buffer_mmaped = true;
> > > +                    break;
> > > +                }
> > > +            }
> > > +        }
> > > +
> > > +        if (!buffer_mmaped) {
> > > +            buf = g_malloc0(data_size);
> > > +            ret = pread(vbasedev->fd, buf, data_size,
> > > +                        region->fd_offset + data_offset);
> > > +            if (ret != data_size) {
> > > +                error_report("Failed to get migration data %d", ret);
> > > +                g_free(buf);
> > > +                return -EINVAL;
> > > +            }
> > > +        }
> > > +
> > > +        qemu_put_be64(f, data_size);
> > > +        qemu_put_buffer(f, buf, data_size);
> > > +
> > > +        if (!buffer_mmaped) {
> > > +            g_free(buf);
> > > +        }
> > > +        migration->pending_bytes -= data_size;
> > > +    } else {
> > > +        qemu_put_be64(f, data_size);
> > > +    }
> > > +
> > > +    ret = qemu_file_get_error(f);
> > > +
> > > +    return data_size;
> > > +}
> > > +
> > > +static int vfio_update_pending(VFIODevice *vbasedev)
> > > +{
> > > +    VFIOMigration *migration = vbasedev->migration;
> > > +    VFIORegion *region = &migration->region.buffer;
> > > +    uint64_t pending_bytes = 0;
> > > +    int ret;
> > > +
> > > +    ret = pread(vbasedev->fd, &pending_bytes, sizeof(pending_bytes),
> > > +                region->fd_offset + offsetof(struct vfio_device_migration_info,
> > > +                                             pending_bytes));
> > > +    if ((ret < 0) || (ret != sizeof(pending_bytes))) {
> > > +        error_report("Failed to get pending bytes %d", ret);
> > > +        migration->pending_bytes = 0;
> > > +        return (ret < 0) ? ret : -EINVAL;
> > > +    }
> > > +
> > > +    migration->pending_bytes = pending_bytes;
> > > +    return 0;
> > > +}
> > > +
> > > +static int vfio_save_device_config_state(QEMUFile *f, void *opaque)
> > > +{
> > > +    VFIODevice *vbasedev = opaque;
> > > +
> > > +    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_CONFIG_STATE);
> > > +
> > > +    if (vbasedev->type == VFIO_DEVICE_TYPE_PCI) {
> > > +        vfio_pci_save_config(vbasedev, f);
> > > +    }
> > > +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> > > +
> > > +    return qemu_file_get_error(f);
> > > +}
> > > +
> > >  /* ---------------------------------------------------------------------- */
> > >  
> > >  static int vfio_save_setup(QEMUFile *f, void *opaque)
> > > @@ -163,9 +268,116 @@ static void vfio_save_cleanup(void *opaque)
> > >      }
> > >  }
> > >  
> > > +static void vfio_save_pending(QEMUFile *f, void *opaque,
> > > +                              uint64_t threshold_size,
> > > +                              uint64_t *res_precopy_only,
> > > +                              uint64_t *res_compatible,
> > > +                              uint64_t *res_postcopy_only)
> > > +{
> > > +    VFIODevice *vbasedev = opaque;
> > > +    VFIOMigration *migration = vbasedev->migration;
> > > +    int ret;
> > > +
> > > +    ret = vfio_update_pending(vbasedev);
> > > +    if (ret) {
> > > +        return;
> > > +    }
> > > +
> > > +    if (vbasedev->device_state & VFIO_DEVICE_STATE_RUNNING) {
> > > +        *res_precopy_only += migration->pending_bytes;
> > > +    } else {
> > > +        *res_postcopy_only += migration->pending_bytes;
> > > +    }
> by definition,
> - res_precopy_only is for data which must be migrated in precopy phase
>    or in stopped state, in other words - before target vm start
> - res_postcopy_only is for data which must be migrated in postcopy phase
>   or in stopped state, in other words - after source vm stop
> So, we can only determining data type by the nature of the data. i.e.
> if it is device state data which must be copied after source vm stop and
> before target vm start, it belongs to res_precopy_only.
> 
> It is not right to determining data type by current device state.

Right; you can determine it by whether postcopy is *enabled* or not.
However, since this isn't ready for postcopy yet anyway, just add it to
res_postcopy_only all the time;  then you can come back to postcopy
later.

Dave

> Thanks
> Yan
> 
> > > +    *res_compatible += 0;
> > > +}
> > > +
> > > +static int vfio_save_iterate(QEMUFile *f, void *opaque)
> > > +{
> > > +    VFIODevice *vbasedev = opaque;
> > > +    VFIOMigration *migration = vbasedev->migration;
> > > +    int ret;
> > > +
> > > +    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_DATA_STATE);
> > > +
> > > +    qemu_mutex_lock(&migration->lock);
> > > +    ret = vfio_save_buffer(f, vbasedev);
> > > +    qemu_mutex_unlock(&migration->lock);
> > > +
> > > +    if (ret < 0) {
> > > +        error_report("vfio_save_buffer failed %s",
> > > +                     strerror(errno));
> > > +        return ret;
> > > +    }
> > > +
> > > +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> > > +
> > > +    ret = qemu_file_get_error(f);
> > > +    if (ret) {
> > > +        return ret;
> > > +    }
> > > +
> > > +    return ret;
> > > +}
> > > +
> > > +static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
> > > +{
> > > +    VFIODevice *vbasedev = opaque;
> > > +    VFIOMigration *migration = vbasedev->migration;
> > > +    int ret;
> > > +
> > > +    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_SAVING);
> > > +    if (ret) {
> > > +        error_report("Failed to set state STOP and SAVING");
> > > +        return ret;
> > > +    }
> > > +
> > > +    ret = vfio_save_device_config_state(f, opaque);
> > > +    if (ret) {
> > > +        return ret;
> > > +    }
> > > +
> > > +    ret = vfio_update_pending(vbasedev);
> > > +    if (ret) {
> > > +        return ret;
> > > +    }
> > > +
> > > +    while (migration->pending_bytes > 0) {
> > > +        qemu_put_be64(f, VFIO_MIG_FLAG_DEV_DATA_STATE);
> > > +        ret = vfio_save_buffer(f, vbasedev);
> > > +        if (ret < 0) {
> > > +            error_report("Failed to save buffer");
> > > +            return ret;
> > > +        } else if (ret == 0) {
> > > +            break;
> > > +        }
> > > +
> > > +        ret = vfio_update_pending(vbasedev);
> > > +        if (ret) {
> > > +            return ret;
> > > +        }
> > > +    }
> > > +
> > > +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> > > +
> > > +    ret = qemu_file_get_error(f);
> > > +    if (ret) {
> > > +        return ret;
> > > +    }
> > > +
> > > +    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOPPED);
> > > +    if (ret) {
> > > +        error_report("Failed to set state STOPPED");
> > > +        return ret;
> > > +    }
> > > +    return ret;
> > > +}
> > > +
> > >  static SaveVMHandlers savevm_vfio_handlers = {
> > >      .save_setup = vfio_save_setup,
> > >      .save_cleanup = vfio_save_cleanup,
> > > +    .save_live_pending = vfio_save_pending,
> > > +    .save_live_iterate = vfio_save_iterate,
> > > +    .save_live_complete_precopy = vfio_save_complete_precopy,
> > >  };
> > >  
> > >  /* ---------------------------------------------------------------------- */
> > > -- 
> > > 2.7.0
> > > 
> > 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK