copy_to_user_page macro is used in mm/memory.c:access_process_vm
function. This function is called from ptrace code (POKETEXT, POKEDATA)
which write data to memory. Microblaze handle physical address for
caches that's why there is virt_to_phys conversion.

There is potential one location which can caused the problem on WB system.

The important is take a look at write PTRACEs requests
(POKE/TEXT, DATA, USR).

Note:
Majority of Microblaze PTRACE code is moved to generic location
in newer kernel version that's why this solution should work on
the newest kernel version too.

linux/io.h is in cacheflush because of mm/nommu.c

Tested on a WB system - hello world debugging.
Signed-off-by: Michal Simek <monstr@monstr.eu>