Re: [PATCH v4 4/6] arm64/dma-mapping: Implement DMA_ATTR_PRIVILEGED

Robin Murphy
2016-07-26T15:05:24Z

Hi Mitch,

On 25/07/16 20:16, Mitchel Humpherys wrote:
> The newly added DMA_ATTR_PRIVILEGED is useful for creating mappings that
> are only accessible to privileged DMA engines. Implement it in
> dma-iommu.c so that the ARM64 DMA IOMMU mapper can make use of it.
>
> Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
> ---
>
> Notes:
> v3..v4
>
> - Reworked against the new dma attrs format
>
> v2..v3
>
> - Renamed and redocumented dma_direction_to_prot.
> - Dropped the stuff making all privileged mappings read-only.
>
> arch/arm64/mm/dma-mapping.c | 6 +++---
> drivers/iommu/dma-iommu.c | 16 +++++++++++-----
> include/linux/dma-iommu.h | 3 ++-
> 3 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index c4284c432ae8..1c6f85c56115 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -556,7 +556,7 @@ static void *__iommu_alloc_attrs(struct device *dev, size_t size,
> unsigned long attrs)
> {
> bool coherent = is_device_dma_coherent(dev);
> - int ioprot = dma_direction_to_prot(DMA_BIDIRECTIONAL, coherent);
> + int ioprot = dma_info_to_prot(DMA_BIDIRECTIONAL, coherent, attrs);
> size_t iosize = size;
> void *addr;
>
> @@ -710,7 +710,7 @@ static dma_addr_t __iommu_map_page(struct device *dev, struct page *page,
> unsigned long attrs)
> {
> bool coherent = is_device_dma_coherent(dev);
> - int prot = dma_direction_to_prot(dir, coherent);
> + int prot = dma_info_to_prot(dir, coherent, attrs);
> dma_addr_t dev_addr = iommu_dma_map_page(dev, page, offset, size, prot);
>
> if (!iommu_dma_mapping_error(dev, dev_addr) &&
> @@ -768,7 +768,7 @@ static int __iommu_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
> __iommu_sync_sg_for_device(dev, sgl, nelems, dir);
>
> return iommu_dma_map_sg(dev, sgl, nelems,
> - dma_direction_to_prot(dir, coherent));
> + dma_info_to_prot(dir, coherent, attrs));
> }
>
> static void __iommu_unmap_sg_attrs(struct device *dev,
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 08a1e2f3690f..5e1e495b35f8 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -129,26 +129,32 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base, u64 size
> EXPORT_SYMBOL(iommu_dma_init_domain);
>
> /**
> - * dma_direction_to_prot - Translate DMA API directions to IOMMU API page flags
> + * dma_info_to_prot - Translate DMA API directions and attributes to IOMMU API
> + * page flags.
> * @dir: Direction of DMA transfer
> * @coherent: Is the DMA master cache-coherent?
> + * @attrs: DMA attributes for the mapping
> *
> * Return: corresponding IOMMU API page protection flags
> */
> -int dma_direction_to_prot(enum dma_data_direction dir, bool coherent)
> +int dma_info_to_prot(enum dma_data_direction dir, bool coherent,
> + unsigned long attrs)
> {
> int prot = coherent ? IOMMU_CACHE : 0;
>

+ if (attrs & DMA_ATTR_PRIVILEGED)
+ prot |= IOMMU_PRIV;
+

then drop the rest of the changes to the switch statement below. It's
taken me an embarrassingly long time to work out why things were blowing
up in __iommu_sync_single_for_device() all with a VA of phys_to_virt(0) ;)

With that change, for the whole series:

Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Robin Murphy <robin.murphy@arm.com>

I guess at this point it may be worth waiting to repost based on -rc1.
Be sure to CC patch 5 to Vinod as the current dmaengine maintainer, as
it's his ack we'll need on that.

Cheers,
Robin.

> switch (dir) {
> case DMA_BIDIRECTIONAL:
> - return prot | IOMMU_READ | IOMMU_WRITE;
> + prot |= IOMMU_READ | IOMMU_WRITE;
> case DMA_TO_DEVICE:
> - return prot | IOMMU_READ;
> + prot |= IOMMU_READ;
> case DMA_FROM_DEVICE:
> - return prot | IOMMU_WRITE;
> + prot |= IOMMU_WRITE;
> default:
> return 0;
> }
> + if (attrs & DMA_ATTR_PRIVILEGED)
> + prot |= IOMMU_PRIV;
> + return prot;
> }
>
> static struct iova *__alloc_iova(struct iova_domain *iovad, size_t size,
> diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
> index 81c5c8d167ad..b367613d49ba 100644
> --- a/include/linux/dma-iommu.h
> +++ b/include/linux/dma-iommu.h
> @@ -32,7 +32,8 @@ void iommu_put_dma_cookie(struct iommu_domain *domain);
> int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base, u64 size);
>
> /* General helpers for DMA-API <-> IOMMU-API interaction */
> -int dma_direction_to_prot(enum dma_data_direction dir, bool coherent);
> +int dma_info_to_prot(enum dma_data_direction dir, bool coherent,
> + unsigned long attrs);
>
> /*
> * These implement the bulk of the relevant DMA mapping callbacks, but require
>