s390/thp: implement pmdp_set_wrprotect()

s390/thp: implement pmdp_set_wrprotect()

commit be3286507dab888d4aad9f91fd6ff5202b24cd5b upstream.

On s390, an architecture-specific implementation of the function
pmdp_set_wrprotect() is missing and the generic version is currently
being used. The generic version does not flush the tlb as it would be
needed on s390 when modifying an active pmd, which can lead to subtle
tlb errors on s390 when using transparent hugepages.

This patch adds an s390-specific implementation of pmdp_set_wrprotect()
including the missing tlb flush.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>