[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>

2 files changed, 64 insertions, 7 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__ */
 
 /*
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 94b8ba2ec857..0744fb3536b1 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -42,9 +42,52 @@ DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
 
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __attribute__((__aligned__(PAGE_SIZE)));
 
-char  empty_zero_page[PAGE_SIZE] __attribute__((__aligned__(PAGE_SIZE)));
+unsigned long empty_zero_page, zero_page_mask;
 EXPORT_SYMBOL(empty_zero_page);
 
+static unsigned long setup_zero_pages(void)
+{
+        struct cpuid cpu_id;
+        unsigned int order;
+        unsigned long size;
+        struct page *page;
+        int i;
+
+        get_cpu_id(&cpu_id);
+        switch (cpu_id.machine) {
+        case 0x9672:    /* g5 */
+        case 0x2064:    /* z900 */
+        case 0x2066:    /* z900 */
+        case 0x2084:    /* z990 */
+        case 0x2086:    /* z990 */
+        case 0x2094:    /* z9-109 */
+        case 0x2096:    /* z9-109 */
+                order = 0;
+                break;
+        case 0x2097:    /* z10 */
+        case 0x2098:    /* z10 */
+        default:
+                order = 2;
+                break;
+        }
+
+        empty_zero_page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
+        if (!empty_zero_page)
+                panic("Out of memory in setup_zero_pages");
+
+        page = virt_to_page((void *) empty_zero_page);
+        split_page(page, order);
+        for (i = 1 << order; i > 0; i--) {
+                SetPageReserved(page);
+                page++;
+        }
+
+        size = PAGE_SIZE << order;
+        zero_page_mask = (size - 1) & PAGE_MASK;
+
+        return 1UL << order;
+}
+
 /*
  * paging_init() sets up the page tables
  */
@@ -92,14 +135,12 @@ void __init mem_init(void)
         max_mapnr = num_physpages = max_low_pfn;
         high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
 
-        /* clear the zero-page */
-        memset(empty_zero_page, 0, PAGE_SIZE);
-
         /* Setup guest page hinting */
         cmma_init();
 
         /* this will put all low memory onto the freelists */
         totalram_pages += free_all_bootmem();
+        totalram_pages -= setup_zero_pages();   /* Setup zeroed pages. */
 
         reservedpages = 0;