flush_dcache_page from user space.

I mmap'ed mmory allocated by kmalloc , to userspace. I can modify data ( in that memory region ) from kernel space or userspace and call flush_dcache_page to get it refected in both kernel and userspace. 1) if i modify a value from userspace, is there any other way to flush dcache page from userspace. What i am looking is to avoid context switch ( to get into kernel only to call flush_dcache_page ) ? Thanks, Ratheesh