[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, 31 insertions, 7 deletions

diff --git a/include/asm-s390/pgtable.h b/include/asm-s390/pgtable.h
index 8f473a718111..65154dc9a9e5 100644
--- a/include/asm-s390/pgtable.h
+++ b/include/asm-s390/pgtable.h
@@ -421,36 +421,54 @@ static inline int pud_bad(pud_t pud)	 { return 0; }
 
 static inline int pgd_present(pgd_t pgd)
 {
+        if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) < _REGION_ENTRY_TYPE_R2)
+                return 1;
         return (pgd_val(pgd) & _REGION_ENTRY_ORIGIN) != 0UL;
 }
 
 static inline int pgd_none(pgd_t pgd)
 {
+        if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) < _REGION_ENTRY_TYPE_R2)
+                return 0;
         return (pgd_val(pgd) & _REGION_ENTRY_INV) != 0UL;
 }
 
 static inline int pgd_bad(pgd_t pgd)
 {
+        /*
+         * With dynamic page table levels the pgd can be a region table
+         * entry or a segment table entry. Check for the bit that are
+         * invalid for either table entry.
+         */
         unsigned long mask =
-                ~_REGION_ENTRY_ORIGIN & ~_REGION_ENTRY_INV &
+                ~_SEGMENT_ENTRY_ORIGIN & ~_REGION_ENTRY_INV &
                 ~_REGION_ENTRY_TYPE_MASK & ~_REGION_ENTRY_LENGTH;
         return (pgd_val(pgd) & mask) != 0;
 }
 
 static inline int pud_present(pud_t pud)
 {
+        if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) < _REGION_ENTRY_TYPE_R3)
+                return 1;
         return (pud_val(pud) & _REGION_ENTRY_ORIGIN) != 0UL;
 }
 
 static inline int pud_none(pud_t pud)
 {
+        if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) < _REGION_ENTRY_TYPE_R3)
+                return 0;
         return (pud_val(pud) & _REGION_ENTRY_INV) != 0UL;
 }
 
 static inline int pud_bad(pud_t pud)
 {
+        /*
+         * With dynamic page table levels the pud can be a region table
+         * entry or a segment table entry. Check for the bit that are
+         * invalid for either table entry.
+         */
         unsigned long mask =
-                ~_REGION_ENTRY_ORIGIN & ~_REGION_ENTRY_INV &
+                ~_SEGMENT_ENTRY_ORIGIN & ~_REGION_ENTRY_INV &
                 ~_REGION_ENTRY_TYPE_MASK & ~_REGION_ENTRY_LENGTH;
         return (pud_val(pud) & mask) != 0;
 }
@@ -535,7 +553,8 @@ static inline int pte_young(pte_t pte)
 
 static inline void pgd_clear_kernel(pgd_t * pgd)
 {
-        pgd_val(*pgd) = _REGION2_ENTRY_EMPTY;
+        if ((pgd_val(*pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
+                pgd_val(*pgd) = _REGION2_ENTRY_EMPTY;
 }
 
 static inline void pgd_clear(pgd_t * pgd)
@@ -549,10 +568,11 @@ static inline void pgd_clear(pgd_t * pgd)
 
 static inline void pud_clear_kernel(pud_t *pud)
 {
-        pud_val(*pud) = _REGION3_ENTRY_EMPTY;
+        if ((pud_val(*pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
+                pud_val(*pud) = _REGION3_ENTRY_EMPTY;
 }
 
-static inline void pud_clear(pud_t * pud)
+static inline void pud_clear(pud_t *pud)
 {
         pud_t *shadow = get_shadow_table(pud);
 
@@ -841,13 +861,17 @@ static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
 
 static inline pud_t *pud_offset(pgd_t *pgd, unsigned long address)
 {
-        pud_t *pud = (pud_t *) pgd_deref(*pgd);
+        pud_t *pud = (pud_t *) pgd;
+        if ((pgd_val(*pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
+                pud = (pud_t *) pgd_deref(*pgd);
         return pud  + pud_index(address);
 }
 
 static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
 {
-        pmd_t *pmd = (pmd_t *) pud_deref(*pud);
+        pmd_t *pmd = (pmd_t *) pud;
+        if ((pud_val(*pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
+                pmd = (pmd_t *) pud_deref(*pud);
         return pmd + pmd_index(address);
 }