[S390] dynamic page tables.

Add support for different number of page table levels dependent
on the highest address used for a process. This will cause a 31 bit
process to use a two level page table instead of the four level page
table that is the default after the pud has been introduced. Likewise
a normal 64 bit process will use three levels instead of four. Only
if a process runs out of the 4 tera bytes which can be addressed with
a three level page table the fourth level is dynamically added. Then
the process can use up to 8 peta byte.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 248a71010700..8053245fe259 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -112,8 +112,9 @@ void __init paging_init(void)
         init_mm.pgd = swapper_pg_dir;
         S390_lowcore.kernel_asce = __pa(init_mm.pgd) & PAGE_MASK;
 #ifdef CONFIG_64BIT
-        S390_lowcore.kernel_asce |= _ASCE_TYPE_REGION2 | _ASCE_TABLE_LENGTH;
-        pgd_type = _REGION2_ENTRY_EMPTY;
+        /* A three level page table (4TB) is enough for the kernel space. */
+        S390_lowcore.kernel_asce |= _ASCE_TYPE_REGION3 | _ASCE_TABLE_LENGTH;
+        pgd_type = _REGION3_ENTRY_EMPTY;
 #else
         S390_lowcore.kernel_asce |= _ASCE_TABLE_LENGTH;
         pgd_type = _SEGMENT_ENTRY_EMPTY;