vfio/mlx5: Add support for READING in chunk mode

Add support for READING in chunk mode.

In case the last SAVE command recognized that there was still some image
to be read, however, there was no available chunk to use for, this task
was delayed for the reader till one chunk will be consumed and becomes
available.

In the above case, a work will be executed to read in the background the
next image from the device.
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20230911093856.81910-9-yishaih@nvidia.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/mlx5/main.c

@@ -160,6 +160,41 @@ mlx5vf_get_data_buff_from_pos(struct mlx5_vf_migration_file *migf, loff_t pos,
 	return found ? buf : NULL;
 }
 
+static void mlx5vf_buf_read_done(struct mlx5_vhca_data_buffer *vhca_buf)
+{
+	struct mlx5_vf_migration_file *migf = vhca_buf->migf;
+
+	if (vhca_buf->stop_copy_chunk_num) {
+		bool is_header = vhca_buf->dma_dir == DMA_NONE;
+		u8 chunk_num = vhca_buf->stop_copy_chunk_num;
+		size_t next_required_umem_size = 0;
+
+		if (is_header)
+			migf->buf_header[chunk_num - 1] = vhca_buf;
+		else
+			migf->buf[chunk_num - 1] = vhca_buf;
+
+		spin_lock_irq(&migf->list_lock);
+		list_del_init(&vhca_buf->buf_elm);
+		if (!is_header) {
+			next_required_umem_size =
+				migf->next_required_umem_size;
+			migf->next_required_umem_size = 0;
+			migf->num_ready_chunks--;
+		}
+		spin_unlock_irq(&migf->list_lock);
+		if (next_required_umem_size)
+			mlx5vf_mig_file_set_save_work(migf, chunk_num,
+						      next_required_umem_size);
+		return;
+	}
+
+	spin_lock_irq(&migf->list_lock);
+	list_del_init(&vhca_buf->buf_elm);
+	list_add_tail(&vhca_buf->buf_elm, &vhca_buf->migf->avail_list);
+	spin_unlock_irq(&migf->list_lock);
+}
+
 static ssize_t mlx5vf_buf_read(struct mlx5_vhca_data_buffer *vhca_buf,
 			       char __user **buf, size_t *len, loff_t *pos)
 {
@@ -195,12 +230,8 @@ static ssize_t mlx5vf_buf_read(struct mlx5_vhca_data_buffer *vhca_buf,
 		copy_len -= page_len;
 	}
 
-	if (*pos >= vhca_buf->start_pos + vhca_buf->length) {
-		spin_lock_irq(&vhca_buf->migf->list_lock);
-		list_del_init(&vhca_buf->buf_elm);
-		list_add_tail(&vhca_buf->buf_elm, &vhca_buf->migf->avail_list);
-		spin_unlock_irq(&vhca_buf->migf->list_lock);
-	}
+	if (*pos >= vhca_buf->start_pos + vhca_buf->length)
+		mlx5vf_buf_read_done(vhca_buf);
 
 	return done;
 }