Re: [PATCH v4 6/6] arm: dma-mapping: updates to limit dma_mask and iommu mapping size

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Hi Murali,

On 23/01/15 22:32, Murali Karicheri wrote:
Limit the dma_mask to minimum of dma_mask and dma_base + size - 1.

Also arm_iommu_create_mapping() has size parameter of size_t and
arm_setup_iommu_dma_ops() can take a value higher than that. So
limit the size to SIZE_MAX.

Signed-off-by: Murali Karicheri <m-karicheri2@xxxxxx>
---
  arch/arm/mm/dma-mapping.c |   10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 7864797..a1f9030 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -2004,6 +2004,13 @@ static bool arm_setup_iommu_dma_ops(struct device *dev, u64 dma_base, u64 size,
  	if (!iommu)
  		return false;

+	/*
+	 * currently arm_iommu_create_mapping() takes a max of size_t
+	 * for size param. So check this limit for now.
+	 */
+	if (size > SIZE_MAX)
+		return false;
+
  	mapping = arm_iommu_create_mapping(dev->bus, dma_base, size);
  	if (IS_ERR(mapping)) {
  		pr_warn("Failed to create %llu-byte IOMMU mapping for device %s\n",
@@ -2053,6 +2060,9 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
  {
  	struct dma_map_ops *dma_ops;

+	/* limit dma_mask to the lower of the two values */
+	*dev->dma_mask = min((*dev->dma_mask), (dma_base + size - 1));
+

Is there any reason not to do this in of_dma_configure? It seems like something everyone could benefit from - I'd cooked up a dodgy workaround for the same issue in my arm64 IOMMU code, but handling it generically in common code would be much nicer.

Robin.

  	dev->archdata.dma_coherent = coherent;
  	if (arm_setup_iommu_dma_ops(dev, dma_base, size, iommu))
  		dma_ops = arm_get_iommu_dma_map_ops(coherent);



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