vfio/mlx5: Introduce vfio precopy ioctl implementation

vfio precopy ioctl returns an estimation of data available for
transferring from the device.

Whenever a user is using VFIO_MIG_GET_PRECOPY_INFO, track the current
state of the device, and if needed, append the dirty data to the
transfer FD data. This is done by saving a middle state.

As mlx5 runs the SAVE command asynchronously, make sure to query for
incremental data only once there is no active save command.
Running both in parallel, might end-up with a failure in the incremental
query command on un-tracked vhca.

Also, a middle state will be saved only after the previous state has
finished its SAVE command and has been fully transferred, this prevents
endless use resources.

Co-developed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20221206083438.37807-11-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/vfio/pci/mlx5/cmd.c b/drivers/vfio/pci/mlx5/cmd.c
index 160fa38fc78d..12e74ecebe64 100644
--- a/drivers/vfio/pci/mlx5/cmd.c
+++ b/drivers/vfio/pci/mlx5/cmd.c
@@ -67,12 +67,25 @@ int mlx5vf_cmd_query_vhca_migration_state(struct mlx5vf_pci_core_device *mvdev,
 {
 	u32 out[MLX5_ST_SZ_DW(query_vhca_migration_state_out)] = {};
 	u32 in[MLX5_ST_SZ_DW(query_vhca_migration_state_in)] = {};
+	bool inc = query_flags & MLX5VF_QUERY_INC;
 	int ret;
 
 	lockdep_assert_held(&mvdev->state_mutex);
 	if (mvdev->mdev_detach)
 		return -ENOTCONN;
 
+	/*
+	 * In case PRE_COPY is used, saving_migf is exposed while device is
+	 * running. Make sure to run only once there is no active save command.
+	 * Running both in parallel, might end-up with a failure in the
+	 * incremental query command on un-tracked vhca.
+	 */
+	if (inc) {
+		ret = wait_for_completion_interruptible(&mvdev->saving_migf->save_comp);
+		if (ret)
+			return ret;
+	}
+
 	MLX5_SET(query_vhca_migration_state_in, in, opcode,
 		 MLX5_CMD_OP_QUERY_VHCA_MIGRATION_STATE);
 	MLX5_SET(query_vhca_migration_state_in, in, vhca_id, mvdev->vhca_id);
@@ -82,6 +95,9 @@ int mlx5vf_cmd_query_vhca_migration_state(struct mlx5vf_pci_core_device *mvdev,
 
 	ret = mlx5_cmd_exec_inout(mvdev->mdev, query_vhca_migration_state, in,
 				  out);
+	if (inc)
+		complete(&mvdev->saving_migf->save_comp);
+
 	if (ret)
 		return ret;