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>

1 files changed, 7 insertions, 0 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))