Subject: [RFC PATCH 3/5] iommu: implement common IOMMU ops for DMA mapping

From: [email-masked] (Laura Abbott)
Date: Fri, 23 Jan 2015 09:42:15 -0800

On 1/12/2015 12:48 PM, Robin Murphy wrote:
> Taking inspiration from the existing arch/arm code, break out some
> generic functions to interface the DMA-API to the IOMMU-API. This will
> do the bulk of the heavy lifting for IOMMU-backed dma-mapping.
>
> Whilst the target is arm64, rather than introduce yet another private
> implementation, place this in common code as the first step towards
> consolidating the numerous versions spread around between architecture
> code and IOMMU drivers.
>
> Signed-off-by: Robin Murphy <[email-masked]>
> ---
>   include/linux/dma-iommu.h |  78 ++++++++
>   lib/Kconfig               |   8 +
>   lib/Makefile              |   1 +
>   lib/dma-iommu.c           | 455 ++++++++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 542 insertions(+)
>   create mode 100644 include/linux/dma-iommu.h
>   create mode 100644 lib/dma-iommu.c
>
> diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
> new file mode 100644
> index 0000000..4515407
> --- /dev/null
> +++ b/include/linux/dma-iommu.h
<snip>
> +
> +struct iommu_dma_mapping *iommu_dma_create_mapping(struct iommu_ops *ops,
> +		dma_addr_t base, size_t size)
> +{
> +	struct iommu_dma_mapping *mapping;
> +	struct iommu_domain *domain;
> +	struct iova_domain *iovad;
> +	struct iommu_domain_geometry *dg;
> +	unsigned long order, base_pfn, end_pfn;
> +
> +	pr_debug("base=%pad\tsize=0x%zx\n", &base, size);
> +	mapping = kzalloc(sizeof(*mapping), GFP_KERNEL);
> +	if (!mapping)
> +		return NULL;
> +
> +	/*
> +	 * HACK: We'd like to ask the relevant IOMMU in ops for a suitable
> +	 * domain, but until that happens, bypass the bus nonsense and create
> +	 * one directly for this specific device/IOMMU combination...
> +	 */
> +	domain = kzalloc(sizeof(*domain), GFP_KERNEL);
> +
> +	if (!domain)
> +		goto out_free_mapping;
> +	domain->ops = ops;
> +
> +	if (ops->domain_init(domain))
> +		goto out_free_mapping;
> +	/*
> +	 * ...and do the bare minimum to sanity-check that the domain allows
> +	 * at least some access to the device...
> +	 */
> +	dg = &domain->geometry;
> +	if (!(base < dg->aperture_end && base + size > dg->aperture_start)) {
> +		pr_warn("DMA range outside IOMMU capability; is DT correct?\n");
> +		goto out_free_mapping;
> +	}

This check seems to always fail with base = 0 because dg->aperture_end is
always going to be 0 as well. base <= dg->aperature_end ?

Thanks,
Laura

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