Re: [PATCH v6 04/20] dma-pool: track decrypted atomic pools and select them via attrs

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Jason Gunthorpe <jgg@ziepe.ca> writes:

> On Thu, Jun 04, 2026 at 02:09:43PM +0530, Aneesh Kumar K.V (Arm) wrote:
>>  struct page *dma_alloc_from_pool(struct device *dev, size_t size,
>> -		void **cpu_addr, gfp_t gfp,
>> +		void **cpu_addr, gfp_t gfp, unsigned long attrs,
>>  		bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t))
>>  {
>> -	struct gen_pool *pool = NULL;
>> +	struct dma_gen_pool *dma_pool = NULL;
>>  	struct page *page;
>>  	bool pool_found = false;
>>  
>> -	while ((pool = dma_guess_pool(pool, gfp))) {
>> +	while ((dma_pool = dma_guess_pool(dma_pool, gfp))) {
>> +
>> +		if (dma_pool->unencrypted != !!(attrs & DMA_ATTR_CC_SHARED))
>> +			continue;
>
> I don't think you should be overloading DMA_ATTR_CC_SHARED like this.
>
> 	/*
> 	 * 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;
> 	}
>
> It is fine to have a bit inside the attrs that is only used by the
> internal logic, but it needs to have a clearer name
> __DMA_ATTR_REQUIRE_CC_SHARED perhaps.
>

Are you suggesting adding another attribute in addition to
DMA_ATTR_CC_SHARED?

Is the idea that __DMA_ATTR_REQUIRE_CC_SHARED would be used in the
allocation path to request a CC_SHARED allocation, while
DMA_ATTR_CC_SHARED would be used in the mapping path to describe the
attribute of the address?



>
> The sashiko note does look legit though:
>
> 	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> 	    !gfpflags_allow_blocking(gfp) && !coherent) {
> 		page = dma_alloc_from_pool(dev, PAGE_ALIGN(size), &cpu_addr,
> 					   gfp, attrs, NULL);
> 		if (!page)
> 			return NULL;
>
> I don't see anything doing the force_dma_unencrypted test along this
> callchain..
>
> I guess it should be done one step up in dma_alloc_attrs() instead of
> in dma_direct_alloc()?
>

Yes, I'll move it there.

-aneesh