dma-mapping: handle vmalloc addresses in dma_common_{mmap,get_sgtable}

xen-swiotlb can use vmalloc backed addresses for dma coherent allocations
and uses the common helpers.  Properly handle them to unbreak Xen on
ARM platforms.

Fixes: 1b65c4e ("swiotlb-xen: use xen_alloc/free_coherent_pages")
Signed-off-by: Roman Skakun <roman_skakun@epam.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
[hch: split the patch, renamed the helpers]
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/ops_helpers.c

@@ -5,14 +5,21 @@
  */
 #include <linux/dma-map-ops.h>
 
+static struct page *dma_common_vaddr_to_page(void *cpu_addr)
+{
+	if (is_vmalloc_addr(cpu_addr))
+		return vmalloc_to_page(cpu_addr);
+	return virt_to_page(cpu_addr);
+}
+
 /*
  * Create scatter-list for the already allocated DMA buffer.
  */
 int dma_common_get_sgtable(struct device *dev, struct sg_table *sgt,
 		 void *cpu_addr, dma_addr_t dma_addr, size_t size,
 		 unsigned long attrs)
 {
-	struct page *page = virt_to_page(cpu_addr);
+	struct page *page = dma_common_vaddr_to_page(cpu_addr);
 	int ret;
 
 	ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
@@ -32,6 +39,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
 	unsigned long user_count = vma_pages(vma);
 	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
 	unsigned long off = vma->vm_pgoff;
+	struct page *page = dma_common_vaddr_to_page(cpu_addr);
 	int ret = -ENXIO;
 
 	vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, attrs);
@@ -43,7 +51,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
 		return -ENXIO;
 
 	return remap_pfn_range(vma, vma->vm_start,
-			page_to_pfn(virt_to_page(cpu_addr)) + vma->vm_pgoff,
+			page_to_pfn(page) + vma->vm_pgoff,
 			user_count << PAGE_SHIFT, vma->vm_page_prot);
 #else
 	return -ENXIO;