Re: [PATCH v4 03/38] iommu: add generic helper for mapping sgtable objects

[Robin Murphy]

On 2020-05-12 10:00 am, Marek Szyprowski wrote:
> struct sg_table is a common structure used for describing a memory
> buffer. It consists of a scatterlist with memory pages and DMA addresses
> (sgl entry), as well as the number of scatterlist entries: CPU pages
> (orig_nents entry) and DMA mapped pages (nents entry).
>
> It turned out that it was a common mistake to misuse nents and orig_nents
> entries, calling mapping functions with a wrong number of entries.
>
> To avoid such issues, lets introduce a common wrapper operating directly
> on the struct sg_table objects, which take care of the proper use of
> the nents and orig_nents entries.

Modulo Joerg's comments,

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

> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> ---
> For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents
> vs. orig_nents misuse' thread:
> https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@xxxxxxxxxxx/T/
> ---
>   include/linux/iommu.h | 16 ++++++++++++++++
>   1 file changed, 16 insertions(+)
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 7cfd2dd..ba662ba 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -478,6 +478,22 @@ extern size_t iommu_map_sg_atomic(struct iommu_domain *domain,
>   extern void iommu_set_fault_handler(struct iommu_domain *domain,
>   			iommu_fault_handler_t handler, void *token);
>   
> +/**
> + * iommu_map_sgtable - Map the given buffer to the IOMMU domain
> + * @domain:	The IOMMU domain to perfor
> + * @iova:	The start addrees to map the buffer
> + * @sgt:	The sg_table object describing the buffer
> + * @prot:	IOMMU protection bits
> + *
> + * Create a mapping at @iova for the buffer described by a scatterlist
> + * stored in the given sg_table object in the provided IOMMU domain.
> + */
> +static inline size_t iommu_map_sgtable(struct iommu_domain *domain,
> +			unsigned long iova, struct sg_table *sgt, int prot)
> +{
> +	return iommu_map_sg(domain, iova, sgt->sgl, sgt->orig_nents, prot);
> +}
> +
>   extern void iommu_get_resv_regions(struct device *dev, struct list_head *list);
>   extern void iommu_put_resv_regions(struct device *dev, struct list_head *list);
>   extern void generic_iommu_put_resv_regions(struct device *dev,