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

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Jun 10, 2026 at 01:37:26PM +0530, Aneesh Kumar K.V wrote:
> 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?

Yeah, it is a thought at least

Maybe a comment is good enough.

I just find it hard to follow when we have this dual usage. Like the
code above for dma_pool->unencrypted is completely wrong if it is an
"attribute of an address". Easy to cut & paste that into the wrong
context.

Especially if you move things up higher.. having the alloc set both
CC_SHARED and REQUIRE_CC_SHARED or maybe ALLOC_CC_SHARED would make it
clearer that the alloc code lives under that callchain

Jason