[PATCH v6 03/20] dma-direct: use DMA_ATTR_CC_SHARED in alloc/free paths

[Petr Tesarik]

On Thu,  4 Jun 2026 14:09:42 +0530
"Aneesh Kumar K.V (Arm)" <aneesh.kumar at kernel.org> wrote:

> Propagate force_dma_unencrypted() into DMA_ATTR_CC_SHARED in the
> dma-direct allocation path and use the attribute to drive the related
> decisions.
> 
> This updates dma_direct_alloc(), dma_direct_free(), and
> dma_direct_alloc_pages() to fold the forced unencrypted case into attrs.
> 
> Tested-by: Jiri Pirko <jiri at nvidia.com>
> Tested-by: Michael Kelley <mhklinux at outlook.com>
> Tested-by: Mostafa Saleh <smostafa at google.com>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar at kernel.org>

Reviewed-by: Petr Tesarik <ptesarik at suse.com>

Petr T

> ---
>  kernel/dma/direct.c | 53 +++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 44 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index a741c8a2ee66..90dc5057a0c0 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -193,16 +193,31 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
>  {
>  	bool remap = false, set_uncached = false;
> -	bool mark_mem_decrypt = true;
> +	bool mark_mem_decrypt = false;
>  	struct page *page;
>  	void *ret;
>  
> +	/*
> +	 * DMA_ATTR_CC_SHARED is not a caller-visible dma_alloc_*()
> +	 * attribute. The direct allocator uses it internally after it has
> +	 * decided that the backing pages must be shared/decrypted, so the
> +	 * rest of the allocation path can consistently select DMA addresses,
> +	 * choose compatible pools and restore encryption on free.
> +	 */
> +	if (attrs & DMA_ATTR_CC_SHARED)
> +		return NULL;
> +
> +	if (force_dma_unencrypted(dev)) {
> +		attrs |= DMA_ATTR_CC_SHARED;
> +		mark_mem_decrypt = true;
> +	}
> +
>  	size = PAGE_ALIGN(size);
>  	if (attrs & DMA_ATTR_NO_WARN)
>  		gfp |= __GFP_NOWARN;
>  
> -	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
> -	    !force_dma_unencrypted(dev) && !is_swiotlb_for_alloc(dev))
> +	if (((attrs & (DMA_ATTR_NO_KERNEL_MAPPING | DMA_ATTR_CC_SHARED)) ==
> +	     DMA_ATTR_NO_KERNEL_MAPPING) && !is_swiotlb_for_alloc(dev))
>  		return dma_direct_alloc_no_mapping(dev, size, dma_handle, gfp);
>  
>  	if (!dev_is_dma_coherent(dev)) {
> @@ -236,7 +251,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  	 * Remapping or decrypting memory may block, allocate the memory from
>  	 * the atomic pools instead if we aren't allowed block.
>  	 */
> -	if ((remap || force_dma_unencrypted(dev)) &&
> +	if ((remap || (attrs & DMA_ATTR_CC_SHARED)) &&
>  	    dma_direct_use_pool(dev, gfp))
>  		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>  
> @@ -312,12 +327,24 @@ void dma_direct_free(struct device *dev, size_t size,
>  		void *cpu_addr, dma_addr_t dma_addr, unsigned long attrs)
>  {
>  	phys_addr_t phys;
> -	bool mark_mem_encrypted = true;
> +	bool mark_mem_encrypted = false;
>  	struct io_tlb_pool *swiotlb_pool;
>  	unsigned int page_order = get_order(size);
>  
> -	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
> -	    !force_dma_unencrypted(dev) && !is_swiotlb_for_alloc(dev)) {
> +	/* see dma_direct_alloc() for details */
> +	WARN_ON(attrs & DMA_ATTR_CC_SHARED);
> +
> +	/*
> +	 * if the device had requested for an unencrypted buffer,
> +	 * convert it to encrypted on free
> +	 */
> +	if (force_dma_unencrypted(dev)) {
> +		attrs |= DMA_ATTR_CC_SHARED;
> +		mark_mem_encrypted = true;
> +	}
> +
> +	if (((attrs & (DMA_ATTR_NO_KERNEL_MAPPING | DMA_ATTR_CC_SHARED)) ==
> +	     DMA_ATTR_NO_KERNEL_MAPPING) && !is_swiotlb_for_alloc(dev)) {
>  		/* cpu_addr is a struct page cookie, not a kernel address */
>  		dma_free_contiguous(dev, cpu_addr, size);
>  		return;
> @@ -366,10 +393,14 @@ void dma_direct_free(struct device *dev, size_t size,
>  struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
>  		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp)
>  {
> +	unsigned long attrs = 0;
>  	struct page *page;
>  	void *ret;
>  
> -	if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
> +	if (force_dma_unencrypted(dev))
> +		attrs |= DMA_ATTR_CC_SHARED;
> +
> +	if ((attrs & DMA_ATTR_CC_SHARED) && dma_direct_use_pool(dev, gfp))
>  		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>  
>  	if (is_swiotlb_for_alloc(dev)) {
> @@ -403,7 +434,11 @@ void dma_direct_free_pages(struct device *dev, size_t size,
>  	phys_addr_t phys;
>  	void *vaddr = page_address(page);
>  	struct io_tlb_pool *swiotlb_pool;
> -	bool mark_mem_encrypted = true;
> +	/*
> +	 * if the device had requested for an unencrypted buffer,
> +	 * convert it to encrypted on free
> +	 */
> +	bool mark_mem_encrypted = force_dma_unencrypted(dev);
>  
>  	/* If cpu_addr is not from an atomic pool, dma_free_from_pool() fails */
>  	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&