fix and improvement of flush(_kernel)_dcache_page()

index e4448e1..eca955f 100644
@@ -307,6 +307,10 @@ static inline void flush_anon_page(struct vm_area_struct *vma,
 #define ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE
 static inline void flush_kernel_dcache_page(struct page *page)
 {
+	extern void __flush_kernel_dcache_page(struct page *);
+	/* highmem pages are always flushed upon kunmap already */
+	if (!PageHighMem(page))
+		__flush_kernel_dcache_page(page);
 }
 
 #define flush_dcache_mmap_lock(mapping) \

index 40ca11e..982db2f 100644
@@ -192,6 +192,45 @@ void __flush_dcache_page(struct address_space *mapping, struct page *page)
 				page->index << PAGE_CACHE_SHIFT);
 }
 
+/*
+ * Ensure cache coherency for the kernel mapping of this page.
+ *
+ * If the page only exists in the page cache and there are no user
+ * space mappings, we can be lazy and remember that we may have dirty
+ * kernel cache lines for later.  Otherwise, we need to flush the
+ * dirty kernel cache lines directly.
+ *
+ * Note that we disable the lazy flush for SMP configurations where
+ * the cache maintenance operations are not automatically broadcasted.
+ *
+ * We can assume that the page is no high mem page, see
+ * flush_kernel_dcache_page.
+ */
+void __flush_kernel_dcache_page(struct page *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);
+
+	if (!cache_ops_need_broadcast() &&
+	    mapping && !mapping_mapped(mapping))
+		clear_bit(PG_dcache_clean, &page->flags);
+	else {
+		__cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
+		if (mapping && !cache_is_vivt())
+			__flush_icache_all();
+		set_bit(PG_dcache_clean, &page->flags);
+	}
+}
+EXPORT_SYMBOL(__flush_kernel_dcache_page);
+
 static void __flush_dcache_aliases(struct address_space *mapping, struct page *page)
 {
 	struct mm_struct *mm = current->active_mm;

index 982db2f..077c8fd 100644
@@ -219,15 +219,18 @@ void __flush_kernel_dcache_page(struct page *page)
 
 	mapping = page_mapping(page);
 
-	if (!cache_ops_need_broadcast() &&
-	    mapping && !mapping_mapped(mapping))
-		clear_bit(PG_dcache_clean, &page->flags);
-	else {
-		__cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
-		if (mapping && !cache_is_vivt())
-			__flush_icache_all();
-		set_bit(PG_dcache_clean, &page->flags);
+	if (!cache_ops_need_broadcast()) {
+		if ((mapping && !mapping_mapped(mapping)) ||
+		    (!mapping && cache_is_vipt_nonaliasing())) {
+			clear_bit(PG_dcache_clean, &page->flags);
+			return;
+		}
 	}
+
+	__cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
+	if (mapping && !cache_is_vivt())
+		__flush_icache_all();
+	set_bit(PG_dcache_clean, &page->flags);
 }
 EXPORT_SYMBOL(__flush_kernel_dcache_page);
 

@@ -296,16 +299,20 @@ void __sync_icache_dcache(pte_t pteval)
  * of this page.
  *
  * We have three cases to consider:
- *  - VIPT non-aliasing cache: fully coherent so nothing required.
+ *  - VIPT non-aliasing cache:
+ *          D-cache: fully coherent so nothing required.
+ *          I-cache: Ensure I/D coherency in case of an already mapped page;
+ *                   __sync_icache_dcache() will handle the other cases.
+ *  - VIPT aliasing:
+ *          D-cache: need to handle one alias in our current VM view.
+ *          I-cache: same as VIPT non-aliasing cache
  *  - VIVT: fully aliasing, so we need to handle every alias in our
  *          current VM view.
- *  - VIPT aliasing: need to handle one alias in our current VM view.
  *
- * If we need to handle aliasing:
- *  If the page only exists in the page cache and there are no user
- *  space mappings, we can be lazy and remember that we may have dirty
- *  kernel cache lines for later.  Otherwise, we assume we have
- *  aliasing mappings.
+ * If the page only exists in the page cache and there are no user
+ * space mappings, we can be lazy and remember that we may have dirty
+ * kernel cache lines for later.  Otherwise, we assume we have
+ * aliasing mappings.
  *
  * Note that we disable the lazy flush for SMP configurations where
  * the cache maintenance operations are not automatically broadcasted.

@@ -323,17 +330,20 @@ void flush_dcache_page(struct page *page)
 
 	mapping = page_mapping(page);
 
-	if (!cache_ops_need_broadcast() &&
-	    mapping && !mapping_mapped(mapping))
-		clear_bit(PG_dcache_clean, &page->flags);
-	else {
-		__flush_dcache_page(mapping, page);
-		if (mapping && cache_is_vivt())
-			__flush_dcache_aliases(mapping, page);
-		else if (mapping)
-			__flush_icache_all();
-		set_bit(PG_dcache_clean, &page->flags);
+	if (!cache_ops_need_broadcast()) {
+		if ((mapping && !mapping_mapped(mapping)) ||
+		    (!mapping && cache_is_vipt_nonaliasing())) {
+			clear_bit(PG_dcache_clean, &page->flags);
+			return;
+		}
 	}
+
+	__flush_dcache_page(mapping, page);
+	if (mapping && cache_is_vivt())
+		__flush_dcache_aliases(mapping, page);
+	else if (mapping)
+		__flush_icache_all();
+	set_bit(PG_dcache_clean, &page->flags);
 }
 EXPORT_SYMBOL(flush_dcache_page);