Re: [RFC PATCH 1/4] dma-buf: heaps: restricted_heap: add no_map attribute

[Christian König <christian.koenig@xxxxxxx>]

Am 30.08.24 um 09:03 schrieb Jens Wiklander:
> Add a no_map attribute to struct restricted_heap_attachment and struct
> restricted_heap to skip the call to dma_map_sgtable() if set. This
> avoids trying to map a dma-buf that doens't refer to memory accessible
> by the kernel.

You seem to have a misunderstanding here dma_map_sgtable() is called to 
map a table into IOMMU and not any kernel address space.

So please explain why you need that?

Regards,
Christian.

> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> ---
>   drivers/dma-buf/heaps/restricted_heap.c | 17 +++++++++++++----
>   drivers/dma-buf/heaps/restricted_heap.h |  2 ++
>   2 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma-buf/heaps/restricted_heap.c b/drivers/dma-buf/heaps/restricted_heap.c
> index 8bc8a5e3f969..4bf28e3727ca 100644
> --- a/drivers/dma-buf/heaps/restricted_heap.c
> +++ b/drivers/dma-buf/heaps/restricted_heap.c
> @@ -16,6 +16,7 @@
>   struct restricted_heap_attachment {
>   	struct sg_table			*table;
>   	struct device			*dev;
> +	bool no_map;
>   };
>   
>   static int
> @@ -54,6 +55,8 @@ restricted_heap_memory_free(struct restricted_heap *rheap, struct restricted_buf
>   static int restricted_heap_attach(struct dma_buf *dmabuf, struct dma_buf_attachment *attachment)
>   {
>   	struct restricted_buffer *restricted_buf = dmabuf->priv;
> +	struct dma_heap *heap = restricted_buf->heap;
> +	struct restricted_heap *rheap = dma_heap_get_drvdata(heap);
>   	struct restricted_heap_attachment *a;
>   	struct sg_table *table;
>   
> @@ -70,6 +73,7 @@ static int restricted_heap_attach(struct dma_buf *dmabuf, struct dma_buf_attachm
>   	sg_dma_mark_restricted(table->sgl);
>   	a->table = table;
>   	a->dev = attachment->dev;
> +	a->no_map = rheap->no_map;
>   	attachment->priv = a;
>   
>   	return 0;
> @@ -92,9 +96,12 @@ restricted_heap_map_dma_buf(struct dma_buf_attachment *attachment,
>   	struct sg_table *table = a->table;
>   	int ret;
>   
> -	ret = dma_map_sgtable(attachment->dev, table, direction, DMA_ATTR_SKIP_CPU_SYNC);
> -	if (ret)
> -		return ERR_PTR(ret);
> +	if (!a->no_map) {
> +		ret = dma_map_sgtable(attachment->dev, table, direction,
> +				      DMA_ATTR_SKIP_CPU_SYNC);
> +		if (ret)
> +			return ERR_PTR(ret);
> +	}
>   	return table;
>   }
>   
> @@ -106,7 +113,9 @@ restricted_heap_unmap_dma_buf(struct dma_buf_attachment *attachment, struct sg_t
>   
>   	WARN_ON(a->table != table);
>   
> -	dma_unmap_sgtable(attachment->dev, table, direction, DMA_ATTR_SKIP_CPU_SYNC);
> +	if (!a->no_map)
> +		dma_unmap_sgtable(attachment->dev, table, direction,
> +				  DMA_ATTR_SKIP_CPU_SYNC);
>   }
>   
>   static int
> diff --git a/drivers/dma-buf/heaps/restricted_heap.h b/drivers/dma-buf/heaps/restricted_heap.h
> index 7dec4b8a471b..94cc0842f70d 100644
> --- a/drivers/dma-buf/heaps/restricted_heap.h
> +++ b/drivers/dma-buf/heaps/restricted_heap.h
> @@ -27,6 +27,8 @@ struct restricted_heap {
>   	unsigned long		cma_paddr;
>   	unsigned long		cma_size;
>   
> +	bool			no_map;
> +
>   	void			*priv_data;
>   };
>