[RFC/PATCHv2 v2 1/4] ARM64: dma: Add support for NO_KERNEL_MAPPING attribute

[Stephen Boyd]

Both the IOMMU and non-IOMMU allocations don't respect the
NO_KERNEL_MAPPING attribute, therefore drivers can't save virtual
address space and time spent mapping large buffers that are
intended only for userspace. Plumb this attribute into the code
for both types of DMA ops.

Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Signed-off-by: Stephen Boyd <stephen.boyd@xxxxxxxxxx>
---
 arch/arm64/mm/dma-mapping.c | 39 ++++++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index a6e757cbab77..9686e722a047 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -169,6 +169,9 @@ static void *__dma_alloc(struct device *dev, size_t size,
 
 	/* create a coherent mapping */
 	page = virt_to_page(ptr);
+	if (dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs))
+		return page;
+
 	coherent_ptr = dma_common_contiguous_remap(page, size, VM_USERMAP,
 						   prot, NULL);
 	if (!coherent_ptr)
@@ -194,7 +197,8 @@ static void __dma_free(struct device *dev, size_t size,
 	if (!is_device_dma_coherent(dev)) {
 		if (__free_from_pool(vaddr, size))
 			return;
-		vunmap(vaddr);
+		if (!dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs))
+			vunmap(vaddr);
 	}
 	__dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs);
 }
@@ -567,6 +571,9 @@ static void *__iommu_alloc_attrs(struct device *dev, size_t size,
 		if (!pages)
 			return NULL;
 
+		if (dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs))
+			return pages;
+
 		addr = dma_common_pages_remap(pages, size, VM_USERMAP, prot,
 					      __builtin_return_address(0));
 		if (!addr)
@@ -624,18 +631,32 @@ static void __iommu_free_attrs(struct device *dev, size_t size, void *cpu_addr,
 		if (WARN_ON(!area || !area->pages))
 			return;
 		iommu_dma_free(dev, area->pages, iosize, &handle);
-		dma_common_free_remap(cpu_addr, size, VM_USERMAP);
+		if (!dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs))
+			dma_common_free_remap(cpu_addr, size, VM_USERMAP);
 	} else {
 		iommu_dma_unmap_page(dev, handle, iosize, 0, NULL);
 		__free_pages(virt_to_page(cpu_addr), get_order(size));
 	}
 }
 
+static struct page **__iommu_get_pages(void *cpu_addr, struct dma_attrs *attrs)
+{
+	struct vm_struct *area;
+
+	if (dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs))
+		return cpu_addr;
+
+	area = find_vm_area(cpu_addr);
+	if (area)
+		return area->pages;
+	return NULL;
+}
+
 static int __iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
 			      void *cpu_addr, dma_addr_t dma_addr, size_t size,
 			      struct dma_attrs *attrs)
 {
-	struct vm_struct *area;
+	struct page **pages;
 	int ret;
 
 	vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot,
@@ -644,11 +665,11 @@ static int __iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
 	if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret))
 		return ret;
 
-	area = find_vm_area(cpu_addr);
-	if (WARN_ON(!area || !area->pages))
+	pages = __iommu_get_pages(cpu_addr, attrs);
+	if (WARN_ON(!pages))
 		return -ENXIO;
 
-	return iommu_dma_mmap(area->pages, size, vma);
+	return iommu_dma_mmap(pages, size, vma);
 }
 
 static int __iommu_get_sgtable(struct device *dev, struct sg_table *sgt,
@@ -656,12 +677,12 @@ static int __iommu_get_sgtable(struct device *dev, struct sg_table *sgt,
 			       size_t size, struct dma_attrs *attrs)
 {
 	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
-	struct vm_struct *area = find_vm_area(cpu_addr);
+	struct page **pages = __iommu_get_pages(cpu_addr, attrs);
 
-	if (WARN_ON(!area || !area->pages))
+	if (WARN_ON(!pages))
 		return -ENXIO;
 
-	return sg_alloc_table_from_pages(sgt, area->pages, count, 0, size,
+	return sg_alloc_table_from_pages(sgt, pages, count, 0, size,
 					 GFP_KERNEL);
 }
 
-- 
2.8.0.rc4