Some questions about high memory

hi all: I am trying to write a driver for my block device which dma support high memory copying. I have register my device as "blk_bounce_any". But my driver cannot see block layer pass high memory to me so far. Is there any user/kernel test program which will purposely send high memory for driver to use? or is there any flag when opening a file in user mode that will use high memory? -- Thanks for your help in advance,