[PATCH 2/2] ARM: DMA: Use vm_pgoff for IOMMU mmap

["Ørjan Eide" <orjan.eide@arm.com>]

arm_iommu_mmap_attrs() ignores the page offset in vma->vm_pgoff that was
specified in the mmap call. Any user of dma_mmap_* will get an
unexpected result when the device uses the IOMMU DMA ops.

Some DRM driver that use dma_mmap_* seems to depend on it ignoring
vma->vm_pgoff.  Both the Samsung Exynos DRM driver before v3.18, and the
current Rockchip DRM driver, use the page offset to pass GEM cookies
that are used to look up the GEM buffers and then call dma_mmap_attrs()
with the cookie value still in vma->vm_pgoff.

rockchip_gem_mmap_buf() in drivers/gpu/drm/rockchip/rockchip_drm_gem.c
still does this. It should be fixed before fixing
arm_iommu_mmap_attrs().

Signed-off-by: Ørjan Eide <orjan.eide@arm.com>
---
 arch/arm/mm/dma-mapping.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index c274476..07d571b 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1364,6 +1364,9 @@ static int arm_iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
 {
 	unsigned long uaddr = vma->vm_start;
 	unsigned long usize = vma->vm_end - vma->vm_start;
+	unsigned long nr_vma_pages = usize >> PAGE_SHIFT;
+	unsigned long nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
+	unsigned long off = vma->vm_pgoff;
 	struct page **pages = __iommu_get_pages(cpu_addr, attrs);
 
 	vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot);
@@ -1371,6 +1374,11 @@ static int arm_iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
 	if (!pages)
 		return -ENXIO;
 
+	if (off >= nr_pages || nr_vma_pages > (nr_pages - off))
+		return -ENXIO;
+
+	pages += off;
+
 	do {
 		int ret = vm_insert_page(vma, uaddr, *pages++);
 		if (ret) {
-- 
1.9.1