ARM: ZERO_PAGE: Avoid flush_dcache_page() for zero page

The zero page is read-only, and has its cache state cleared during
boot.  No further maintanence for this page is required.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

3 files changed, 18 insertions, 2 deletions

diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index d0d17b6a3703..4fbc7de8b4ac 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -151,7 +151,14 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
         if (!pfn_valid(pfn))
                 return;
 
+        /*
+         * The zero page is never written to, so never has any dirty
+         * cache lines, and therefore never needs to be flushed.
+         */
         page = pfn_to_page(pfn);
+        if (page == ZERO_PAGE(0))
+                return;
+
         mapping = page_mapping(page);
 #ifndef CONFIG_SMP
         if (test_and_clear_bit(PG_dcache_dirty, &page->flags))
diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index 43474d8752a6..82f4b06bf6b4 100644
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -189,7 +189,16 @@ static void __flush_dcache_aliases(struct address_space *mapping, struct page *p
  */
 void flush_dcache_page(struct page *page)
 {
-        struct address_space *mapping = page_mapping(page);
+        struct address_space *mapping;
+
+        /*
+         * The zero page is never written to, so never has any dirty
+         * cache lines, and therefore never needs to be flushed.
+         */
+        if (page == ZERO_PAGE(0))
+                return;
+
+        mapping = page_mapping(page);
 
 #ifndef CONFIG_SMP
         if (!PageHighMem(page) && mapping && !mapping_mapped(mapping))
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index ea67be0223ac..2427cdcd9098 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1036,7 +1036,7 @@ void __init paging_init(struct machine_desc *mdesc)
          */
         zero_page = alloc_bootmem_low_pages(PAGE_SIZE);
         empty_zero_page = virt_to_page(zero_page);
-        flush_dcache_page(empty_zero_page);
+        __flush_dcache_page(NULL, empty_zero_page);
 }
 
 /*