[S390] zero page cache synonyms

If the zero page is mapped to virtual user space addresses that differ
only in bit 2^12 or 2^13 we get L1 cache synonyms which can affect
performance. Follow the mips model and use multiple zero pages to avoid
the synonyms.

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

1 files changed, 19 insertions, 3 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 3157441ee1da..22a294571000 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -46,11 +46,27 @@ extern void vmem_map_init(void);
 #define update_mmu_cache(vma, address, ptep)     do { } while (0)
 
 /*
- * ZERO_PAGE is a global shared page that is always zero: used
+ * ZERO_PAGE is a global shared page that is always zero; used
  * for zero-mapped memory areas etc..
  */
-extern char empty_zero_page[PAGE_SIZE];
-#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
+
+extern unsigned long empty_zero_page;
+extern unsigned long zero_page_mask;
+
+#define ZERO_PAGE(vaddr) \
+        (virt_to_page((void *)(empty_zero_page + \
+         (((unsigned long)(vaddr)) &zero_page_mask))))
+
+#define is_zero_pfn is_zero_pfn
+static inline int is_zero_pfn(unsigned long pfn)
+{
+        extern unsigned long zero_pfn;
+        unsigned long offset_from_zero_pfn = pfn - zero_pfn;
+        return offset_from_zero_pfn <= (zero_page_mask >> PAGE_SHIFT);
+}
+
+#define my_zero_pfn(addr)       page_to_pfn(ZERO_PAGE(addr))
+
 #endif /* !__ASSEMBLY__ */
 
 /*