[S390] store indication fault optimization

Use the store indication bit in the translation exception code on
page faults to avoid the protection faults that immediatly follow
the page fault if the access has been a write.

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

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 785229ae39cba424fd523feb556c2c54123ab498..85cd4b039de6b90e998185566e8b2f0c78252ac9 100644 (file)
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -38,6 +38,7 @@
 extern pgd_t swapper_pg_dir[] __attribute__ ((aligned (4096)));
 extern void paging_init(void);
 extern void vmem_map_init(void);
+extern void fault_init(void);
 
 /*
  * The S390 doesn't have any external MMU info: the kernel page

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 2505b2ea0ef187803033c096bab3cff8eac45f02..b49d12073f1046b062876ae2a79edc0faa8c3940 100644 (file)
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -52,6 +52,19 @@
 #define VM_FAULT_BADMAP                0x020000
 #define VM_FAULT_BADACCESS     0x040000
 
+static unsigned long store_indication;
+
+void fault_init(void)
+{
+       unsigned long long facility_list[2];
+
+       if (stfle(facility_list, 2) < 2)
+               return;
+       if ((facility_list[0] & (1ULL << 61)) &&
+           (facility_list[1] & (1ULL << 52)))
+               store_indication = 0xc00;
+}
+
 static inline int notify_page_fault(struct pt_regs *regs)
 {
        int ret = 0;
@@ -294,7 +307,7 @@ static inline int do_exception(struct pt_regs *regs, int access,
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        unsigned long address;
-       int fault;
+       int fault, write;
 
        if (notify_page_fault(regs))
                return 0;
@@ -348,8 +361,10 @@ static inline int do_exception(struct pt_regs *regs, int access,
         * make sure we exit gracefully rather than endlessly redo
         * the fault.
         */
-       fault = handle_mm_fault(mm, vma, address,
-                               (access == VM_WRITE) ? FAULT_FLAG_WRITE : 0);
+       write = (access == VM_WRITE ||
+                (trans_exc_code & store_indication) == 0x400) ?
+               FAULT_FLAG_WRITE : 0;
+       fault = handle_mm_fault(mm, vma, address, write);
        if (unlikely(fault & VM_FAULT_ERROR))
                goto out_up;
 

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 852a3fec1ecef7b493fb5c64dd19a8a8155f7202..bb409332a484add0f68a1c20734d81968273f0e6 100644 (file)
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -124,6 +124,7 @@ void __init paging_init(void)
 #endif
        max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
        free_area_init_nodes(max_zone_pfns);
+       fault_init();
 }
 
 void __init mem_init(void)