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

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Message-ID: <06570238-04a9-47ca-e6e2-c69606635446@arm.com>
Date:   Thu, 7 Apr 2022 14:07:21 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Mario Limonciello <mario.limonciello@....com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>
Cc:     Hegde Vasant <Vasant.Hegde@....com>,
        open list <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH v2 2/2] dma-iommu: Check that swiotlb is active before
 trying to use it

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@....com>

> 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);