ion: use alloc_pages in system contig heap

There is no reason to use kzalloc, just call alloc_pages directly.
Change the GFP from GFP_KERNEL to include __GFP_HIGH, to allow it
to return contiguous pages from highmem.  virt_to_* functions
aren't valid on highmem pages, so store the struct page * in an
sg_table in buffer->priv_virt like most other heaps, and replace
virt_to_* with page_to_*.

Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion_system_heap.c

@@ -360,29 +360,69 @@ static int ion_system_contig_heap_allocate(struct ion_heap *heap,
 					   unsigned long flags)
 {
 	int order = get_order(len);
+	struct page *page;
+	struct sg_table *table;
+	unsigned long i;
+	int ret;
 
 	if (align > (PAGE_SIZE << order))
 		return -EINVAL;
 
-	if (ion_buffer_fault_user_mappings(buffer))
-		return -EINVAL;
-
-	buffer->priv_virt = kzalloc(len, GFP_KERNEL);
-	if (!buffer->priv_virt)
+	page = alloc_pages(low_order_gfp_flags, order);
+	if (!page)
 		return -ENOMEM;
+
+	split_page(page, order);
+
+	len = PAGE_ALIGN(len);
+	for (i = len >> PAGE_SHIFT; i < (1 << order); i++)
+		__free_page(page + i);
+
+	table = kzalloc(sizeof(struct sg_table), GFP_KERNEL);
+	if (!table) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = sg_alloc_table(table, 1, GFP_KERNEL);
+	if (ret)
+		goto out;
+
+	sg_set_page(table->sgl, page, len, 0);
+
+	buffer->priv_virt = table;
+
+	ion_pages_sync_for_device(NULL, page, len, DMA_BIDIRECTIONAL);
+
 	return 0;
+
+out:
+	for (i = 0; i < len >> PAGE_SHIFT; i++)
+		__free_page(page + i);
+	kfree(table);
+	return ret;
 }
 
 void ion_system_contig_heap_free(struct ion_buffer *buffer)
 {
-	kfree(buffer->priv_virt);
+	struct sg_table *table = buffer->priv_virt;
+	struct page *page = sg_page(table->sgl);
+	unsigned long pages = PAGE_ALIGN(buffer->size) >> PAGE_SHIFT;
+	unsigned long i;
+
+	for (i = 0; i < pages; i++)
+		__free_page(page + i);
+	sg_free_table(table);
+	kfree(table);
 }
 
 static int ion_system_contig_heap_phys(struct ion_heap *heap,
 				       struct ion_buffer *buffer,
 				       ion_phys_addr_t *addr, size_t *len)
 {
-	*addr = virt_to_phys(buffer->priv_virt);
+	struct sg_table *table = buffer->priv_virt;
+	struct page *page = sg_page(table->sgl);
+	*addr = page_to_phys(page);
 	*len = buffer->size;
 	return 0;
 }
@@ -390,27 +430,12 @@ static int ion_system_contig_heap_phys(struct ion_heap *heap,
 struct sg_table *ion_system_contig_heap_map_dma(struct ion_heap *heap,
 						struct ion_buffer *buffer)
 {
-	struct sg_table *table;
-	int ret;
-
-	table = kzalloc(sizeof(struct sg_table), GFP_KERNEL);
-	if (!table)
-		return ERR_PTR(-ENOMEM);
-	ret = sg_alloc_table(table, 1, GFP_KERNEL);
-	if (ret) {
-		kfree(table);
-		return ERR_PTR(ret);
-	}
-	sg_set_page(table->sgl, virt_to_page(buffer->priv_virt), buffer->size,
-		    0);
-	return table;
+	return buffer->priv_virt;
 }
 
 void ion_system_contig_heap_unmap_dma(struct ion_heap *heap,
 				      struct ion_buffer *buffer)
 {
-	sg_free_table(buffer->sg_table);
-	kfree(buffer->sg_table);
 }
 
 static struct ion_heap_ops kmalloc_ops = {