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From: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
To: Mostafa Saleh <smostafa@google.com>
Cc: iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev,
	Robin Murphy <robin.murphy@arm.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Steven Price <steven.price@arm.com>,
	Suzuki K Poulose <Suzuki.Poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Jiri Pirko <jiri@resnulli.us>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Petr Tesarik <ptesarik@suse.com>,
	Alexey Kardashevskiy <aik@amd.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Xu Yilun <yilun.xu@linux.intel.com>,
	linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>, x86@kernel.org,
	Jason Gunthorpe <jgg@nvidia.com>,
	Jiri Pirko <jiri@nvidia.com>,
	Michael Kelley <mhklinux@outlook.com>
Subject: Re: [PATCH v8 15/23] dma-direct: pass attrs to dma_capable() for
 DMA_ATTR_CC_SHARED checks
In-Reply-To: <ami9CIGanuQX3lxb@google.com>
References: <20260717180442.110954-1-aneesh.kumar@kernel.org>
 <20260717180442.110954-16-aneesh.kumar@kernel.org>
 <ami9CIGanuQX3lxb@google.com>
Date: Wed, 29 Jul 2026 14:39:08 +0530
Message-ID: <yq5a33x2go23.fsf@kernel.org>
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Mostafa Saleh <smostafa@google.com> writes:

>>  static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size,
>> -		bool is_ram)
>> +		bool is_ram, unsigned long attrs)
>>  {
>>  	dma_addr_t end = addr + size - 1;
>>  
>>  	if (addr == DMA_MAPPING_ERROR)
>>  		return false;
>> +	/*
>> +	 * The DMA address was derived from encrypted RAM, but this device
>> +	 * requires unencrypted DMA addresses. Treat it as not DMA-capable
>> +	 * so the caller can fall back to a suitable SWIOTLB pool.
>> +	 */
>> +	if (!(attrs & DMA_ATTR_CC_SHARED) && force_dma_unencrypted(dev))
>> +		return false;
>> +
>
> I guess it does not make sense to check the other way? I'd be worried if
> some a confidential device uses shared memory which might leak info.
>

>From the perspective of the dma_capable() check, this should be allowed;
that is, a trusted device is permitted to access shared memory.

-aneesh