Re: [PATCH v2 6/8] dma-direct: make dma_direct_map_phys() honor DMA_ATTR_CC_SHARED

[Jason Gunthorpe]

On Mon, Apr 20, 2026 at 11:44:13AM +0530, Aneesh Kumar K.V (Arm) wrote:
> Teach dma_direct_map_phys() to select the DMA address encoding based on
> DMA_ATTR_CC_SHARED.
> 
> Use phys_to_dma_unencrypted() for decrypted mappings and
> phys_to_dma_encrypted() otherwise. If a device requires unencrypted DMA
> but the source physical address is still encrypted, force the mapping
> through swiotlb so the DMA address and backing memory attributes remain
> consistent.
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@xxxxxxxxxx>
> ---
>  kernel/dma/direct.h | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
> index 7140c208c123..928671ef01e9 100644
> --- a/kernel/dma/direct.h
> +++ b/kernel/dma/direct.h
> @@ -86,9 +86,14 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
>  		phys_addr_t phys, size_t size, enum dma_data_direction dir,
>  		unsigned long attrs, bool flush)
>  {
> +	bool force_swiotlb_map = false;
>  	dma_addr_t dma_addr;
>  
> -	if (is_swiotlb_force_bounce(dev)) {
> +	/* if phys addr attribute is encrypted but the device is forcing an encrypted dma addr */
> +	if (!(attrs & DMA_ATTR_CC_SHARED) && force_dma_unencrypted(dev))
> +		force_swiotlb_map = true;

continuing my prior email.. This is really in the wrong spot, it
should be in dma_capable()

> +	if (is_swiotlb_force_bounce(dev) || force_swiotlb_map) {
>  		if (!(attrs & DMA_ATTR_CC_SHARED)) {
>  			if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
>  				return DMA_MAPPING_ERROR;
> @@ -105,18 +110,16 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
>  			goto err_overflow;
>  	} else if (attrs & DMA_ATTR_CC_SHARED) {
>  		dma_addr = phys_to_dma_unencrypted(dev, phys);
> -		if (unlikely(!dma_capable(dev, dma_addr, size, false)))
> -			goto err_overflow;
>  	} else {
> -		dma_addr = phys_to_dma(dev, phys);
> -		if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
> -		    dma_kmalloc_needs_bounce(dev, size, dir)) {

here.

swiotlb because the device can't reach a high address and swiotlb
because the device doesn't have T=1 are really the same thing and
should have the same code flow.

Add attrs to dma_capable() and check force_dma_unencrypted(dev)
inside.

> -			if (is_swiotlb_active(dev) &&
> -			    !(attrs & DMA_ATTR_REQUIRE_COHERENT))
> -				return swiotlb_map(dev, phys, size, dir, attrs);
> +		dma_addr = phys_to_dma_encrypted(dev, phys);
> +	}
>  
> -			goto err_overflow;
> -		}
> +	if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
> +	    dma_kmalloc_needs_bounce(dev, size, dir)) {
> +		if (is_swiotlb_active(dev) &&
> +		    !(attrs & DMA_ATTR_REQUIRE_COHERENT))
> +			return swiotlb_map(dev, phys, size, dir, attrs);
> +		goto err_overflow;
>  	}

Then this movement shouldn't be needed?

Jason