Re: [PATCH v2 2/2] dma-iommu: Check that swiotlb is active before trying to use it

From: Robin Murphy
Date: Thu Apr 07 2022 - 09:07:38 EST

On 2022-04-04 21:47, Mario Limonciello via iommu wrote:
If the IOMMU is in use and an untrusted device is connected to an external
facing port but the address requested isn't page aligned will cause the
kernel to attempt to use bounce buffers.

If for some reason the bounce buffers have not been allocated this is a
problem that should be made apparent to the user.

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
* Move error message into the caller

drivers/iommu/dma-iommu.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 09f6e1c0f9c0..1ca85d37eeab 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -971,6 +971,11 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
void *padding_start;
size_t padding_size, aligned_size;
+ if (!is_swiotlb_active(dev)) {
+ dev_warn_once(dev, "DMA bounce buffers are inactive, unable to map unaligned transaction.\n");
+ }
aligned_size = iova_align(iovad, size);
phys = swiotlb_tbl_map_single(dev, phys, size, aligned_size,
iova_mask(iovad), dir, attrs);