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

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Date:   Mon, 4 Apr 2022 15:47:23 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>
CC:     Christoph Hellwig <hch@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Suthikulpanit Suravee <Suravee.Suthikulpanit@....com>,
        Hegde Vasant <Vasant.Hegde@....com>,
        "open list" <linux-kernel@...r.kernel.org>,
        Mario Limonciello <mario.limonciello@....com>
Subject: [PATCH v2 2/2] dma-iommu: Check that swiotlb is active before trying to use it

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.

Signed-off-by: Mario Limonciello <mario.limonciello@....com>
---
v1->v2:
 * 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");
+			return DMA_MAPPING_ERROR;
+		}
+
 		aligned_size = iova_align(iovad, size);
 		phys = swiotlb_tbl_map_single(dev, phys, size, aligned_size,
 					      iova_mask(iovad), dir, attrs);
-- 
2.34.1