From: Jason Gunthorpe <jgg@ziepe•ca>
To: "Aneesh Kumar K.V" <aneesh.kumar@kernel•org>
Cc: Mostafa Saleh <smostafa@google•com>,
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>, 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
Subject: Re: [PATCH v4 04/13] dma: swiotlb: track pool encryption state and honor DMA_ATTR_CC_SHARED
Date: Wed, 20 May 2026 10:40:39 -0300 [thread overview]
Message-ID: <20260520134039.GT7702@ziepe.ca> (raw)
In-Reply-To: <yq5a5x4ispg8.fsf@kernel.org>
On Wed, May 20, 2026 at 09:27:27AM +0530, Aneesh Kumar K.V wrote:
> Jason Gunthorpe <jgg@ziepe•ca> writes:
>
> > On Tue, May 19, 2026 at 09:35:30PM +0530, Aneesh Kumar K.V wrote:
> >> Yes, that also resulted in simpler and cleaner code.
> >>
> >> swiotlb_tbl_map_single
> >> /*
> >> * If the physical address is encrypted but the device requires
> >> * decrypted DMA, use a decrypted io_tlb_mem and update the
> >> * attributes so the caller knows that a decrypted io_tlb_mem
> >> * was used.
> >> */
> >> if (!(*attrs & DMA_ATTR_CC_SHARED) && force_dma_unencrypted(dev))
> >> *attrs |= DMA_ATTR_CC_SHARED;
> >>
> >> if (mem->unencrypted != !!(*attrs & DMA_ATTR_CC_SHARED))
> >> return (phys_addr_t)DMA_MAPPING_ERROR;
> >
> > Yeah, exactly that is so much clearer now that the mem->unecrypted is
> > tied directly.
> >
> > That logic is reversed though, the incoming ATTR_CC doesn't matter for
> > swiotlb, that is just the source of the memcpy.
> >
> > /* swiotlb pool is incorrect for this device */
> > if (mem->unencrypted != force_dma_unencrypted(dev))
> > return (phys_addr_t)DMA_MAPPING_ERROR;
> >
> > /* Force attrs to match the kind of memory in the pool */
> > if (mem->unencrypted)
> > *attrs |= DMA_ATTR_CC_SHARED;
> > else
> > *attrs &= ~DMA_ATTR_CC_SHARED;
> >
> >
> > Attrs should be forced to whatever memory swiotlb selected.
> >
>
> But that will not handle a T=1 device that wants to use swiotlb to
> bounce unencrypted memory. That is:
>
> force_dma_unencrypted(dev) == 0 /* T=1 device */
> attrs = DMA_ATTR_CC_SHARED;
>
> In that case, it should use an unencrypted io_tlb_mem:
> mem->unencrypted == 1
No! The DMA_ATTR_CC_SHARED only states the nature of the source
memory, the DMA transfer will always happen under T=1
It is perfectly fine to memcpy from shared to private and do a T=1 DMA
from the private memory if we have to bounce.
Jason
next prev parent reply other threads:[~2026-05-20 13:40 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-12 9:03 [PATCH v4 00/13] dma-mapping: Use DMA_ATTR_CC_SHARED through direct, pool and swiotlb paths Aneesh Kumar K.V (Arm)
2026-05-12 9:03 ` [PATCH v4 01/13] dma-direct: swiotlb: handle swiotlb alloc/free outside __dma_direct_alloc_pages Aneesh Kumar K.V (Arm)
2026-05-13 13:57 ` Mostafa Saleh
2026-05-14 4:54 ` Aneesh Kumar K.V
2026-05-12 9:03 ` [PATCH v4 02/13] dma-direct: use DMA_ATTR_CC_SHARED in alloc/free paths Aneesh Kumar K.V (Arm)
2026-05-13 13:58 ` Mostafa Saleh
2026-05-14 5:01 ` Aneesh Kumar K.V
2026-05-12 9:03 ` [PATCH v4 03/13] dma-pool: track decrypted atomic pools and select them via attrs Aneesh Kumar K.V (Arm)
2026-05-13 14:00 ` Mostafa Saleh
2026-05-14 7:00 ` Aneesh Kumar K.V
2026-05-14 8:06 ` Mostafa Saleh
2026-05-16 12:53 ` Alexey Kardashevskiy
2026-05-18 8:19 ` Alexey Kardashevskiy
2026-05-18 8:32 ` Aneesh Kumar K.V
2026-05-12 9:03 ` [PATCH v4 04/13] dma: swiotlb: track pool encryption state and honor DMA_ATTR_CC_SHARED Aneesh Kumar K.V (Arm)
2026-05-13 14:27 ` Mostafa Saleh
2026-05-13 17:24 ` Jason Gunthorpe
2026-05-14 6:24 ` Aneesh Kumar K.V
2026-05-14 11:48 ` Mostafa Saleh
2026-05-14 12:35 ` Jason Gunthorpe
[not found] ` <agXfm3mS_M3fvRrN@google.com>
2026-05-15 22:51 ` Jason Gunthorpe
2026-05-19 11:06 ` Mostafa Saleh
2026-05-19 13:39 ` Jason Gunthorpe
2026-05-14 5:54 ` Aneesh Kumar K.V
2026-05-14 12:02 ` Mostafa Saleh
2026-05-14 12:48 ` Aneesh Kumar K.V
2026-05-14 14:21 ` Mostafa Saleh
2026-05-14 14:43 ` Aneesh Kumar K.V
2026-05-19 11:04 ` Mostafa Saleh
2026-05-19 12:27 ` Aneesh Kumar K.V
2026-05-19 15:07 ` Aneesh Kumar K.V
2026-05-19 15:27 ` Jason Gunthorpe
2026-05-19 16:05 ` Aneesh Kumar K.V
2026-05-19 16:11 ` Jason Gunthorpe
2026-05-20 3:57 ` Aneesh Kumar K.V
2026-05-20 13:40 ` Jason Gunthorpe [this message]
2026-05-19 13:29 ` Jason Gunthorpe
2026-05-19 13:41 ` Mostafa Saleh
2026-05-19 14:00 ` Aneesh Kumar K.V
2026-05-19 14:04 ` Mostafa Saleh
2026-05-19 14:17 ` Aneesh Kumar K.V
2026-05-19 14:27 ` Mostafa Saleh
2026-05-19 14:37 ` Jason Gunthorpe
2026-05-19 14:35 ` Jason Gunthorpe
2026-05-19 14:45 ` Mostafa Saleh
2026-05-19 14:49 ` Jason Gunthorpe
2026-05-14 14:37 ` Jason Gunthorpe
2026-05-18 8:19 ` Alexey Kardashevskiy
2026-05-21 17:06 ` Mostafa Saleh
2026-05-21 17:20 ` Aneesh Kumar K.V
2026-05-12 9:04 ` [PATCH v4 05/13] dma-mapping: make dma_pgprot() " Aneesh Kumar K.V (Arm)
2026-05-12 9:04 ` [PATCH v4 06/13] dma-direct: pass attrs to dma_capable() for DMA_ATTR_CC_SHARED checks Aneesh Kumar K.V (Arm)
2026-05-12 9:04 ` [PATCH v4 07/13] dma-direct: make dma_direct_map_phys() honor DMA_ATTR_CC_SHARED Aneesh Kumar K.V (Arm)
2026-05-18 10:04 ` Christian Borntraeger
2026-05-21 15:37 ` Aneesh Kumar K.V
2026-05-12 9:04 ` [PATCH v4 08/13] dma-direct: set decrypted flag for remapped DMA allocations Aneesh Kumar K.V (Arm)
2026-05-12 9:04 ` [PATCH v4 09/13] dma-direct: select DMA address encoding from DMA_ATTR_CC_SHARED Aneesh Kumar K.V (Arm)
2026-05-12 9:04 ` [PATCH v4 10/13] dma-pool: fix page leak in atomic_pool_expand() cleanup Aneesh Kumar K.V (Arm)
2026-05-12 9:04 ` [PATCH v4 11/13] dma-direct: rename ret to cpu_addr in alloc helpers Aneesh Kumar K.V (Arm)
2026-05-12 9:04 ` [PATCH v4 12/13] dma-direct: return struct page from dma_direct_alloc_from_pool() Aneesh Kumar K.V (Arm)
2026-05-12 9:04 ` [PATCH v4 13/13] x86/amd-gart: preserve the direct DMA address until GART mapping succeeds Aneesh Kumar K.V (Arm)
2026-05-21 11:54 ` Aneesh Kumar K.V
2026-05-17 6:19 ` [PATCH v4 00/13] dma-mapping: Use DMA_ATTR_CC_SHARED through direct, pool and swiotlb paths Jiri Pirko
2026-05-18 8:23 ` Aneesh Kumar K.V
2026-05-18 8:34 ` Jiri Pirko
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