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Mon, 06 Jul 2026 12:52:09 -0700 (PDT) Received: from ziepe.ca ([159.2.72.92]) by smtp.gmail.com with ESMTPSA id af79cd13be357-92e90b800efsm972606685a.4.2026.07.06.12.52.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Jul 2026 12:52:08 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wgpMO-00000000etJ-0DJM; Mon, 06 Jul 2026 16:52:08 -0300 Date: Mon, 6 Jul 2026 16:52:08 -0300 From: Jason Gunthorpe To: Tom Lendacky Cc: Alexey Kardashevskiy , "Aneesh Kumar K.V" , Catalin Marinas , iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, Robin Murphy , Marek Szyprowski , Will Deacon , Marc Zyngier , Steven Price , Suzuki K Poulose , Jiri Pirko , Mostafa Saleh , Petr Tesarik , Dan Williams , Xu Yilun , linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , x86@kernel.org Subject: Re: [PATCH v6 00/20] dma-mapping: Use DMA_ATTR_CC_SHARED through direct, pool and swiotlb paths Message-ID: <20260706195208.GD118978@ziepe.ca> References: <20260618153705.GH231643@ziepe.ca> <20260619122148.GL231643@ziepe.ca> <20260619140616.GB1068655@ziepe.ca> <20260630174216.GK7525@ziepe.ca> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jul 06, 2026 at 01:45:33PM -0500, Tom Lendacky wrote: > In that situation, with SME enabled on the host, the SWIOTLB must be > mapped by the kernel without the encryption bit set and DMA addresses > must be provided to devices without the encryption bit set. This is > because if SWIOTLB is mapped encrypted, requiring the encryption bit be > part of the DMA address, any device that cannot perform DMA at the > address width where the encryption bit exists will fail to DMA properly. Ideally there would be two SWIOTLBs and "decrypted" aka low address, one is only used if the device requires it. Alternatively we don't support this questionable security choice and using swiotlb with an incapable device just fails. Use the iommu, or don't force swiotlb. Jason