arm64: copy_from_user access the last page of ddr has problem on 4.14 kernel

[Kassey]

Hi, Will and team:

   we met a issue when copy_from_user to access the last page of DDR
on 4.14 kenrel, below is the detail steps,
   can you help to suggest if there is know fix or debug something ?

1. we mmap ( in userspace)  a region of  phy address that is not
continous  but include the last page of ddr

  for example our ddr end is 0x200000000
  the last page is fall in below addr:
  0x1fffff000  to  0x200000000

2. we using copy_from_user to copy these mmap address to kernel buffer

3. and we find everytime when trying to copy_from_user  the last page
in phy of ddr,
    the dst kernel buffer is looks overwrite by some same patten start
with "mmap" in this last page ,but the src in the last page of ddr is
still correct.

is there any know issue for copy_from_user to accces the last page of
phy ddr mmaped by userspace  ?



-- 
Best regards
Kassey