User space memory

Hi all, I have some problems allocation Memory the right way and use it in my kernel module. I use a char device for reading and writing from/to a pcie dma card. Especially the read function makes me some headache. The user allocates some memory with posix_memalign and call the read function on the device, so that the devices knows where to write to. My driver now uses get_user_pages() to pin the user pages. The memory has never been written or read by the user, so it's not yet in the RAM, right? And get_user_pages returns a valid number of pages, but for every page the same struct. (respectively the same pointer). Is there any way to ensure that the user pages are in the ram and get_user_pages returns a valid page array? Regards Chris