From: Jason Gunthorpe <jgg@nvidia.com>
To: Shameer Kolothum Thodi <skolothumtho@nvidia.com>
Cc: Nicolin Chen <nicolinc@nvidia.com>,
Catalin Marinas <catalin.marinas@arm.com>,
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"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
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Sonang Patel <sonangp@nvidia.com>,
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Subject: Re: [PATCH v1 4/8] dma-mapping: Keep DMA memory private for capable devices
Date: Wed, 28 Oct 2026 09:38:12 -0300 [thread overview]
Message-ID: <20261028123812.GB2541714@nvidia.com> (raw)
In-Reply-To: <SJ0PR12MB86145DBCF2ADDF3B85719531AB6F2@SJ0PR12MB8614.namprd12.prod.outlook.com>
On Wed, Oct 28, 2026 at 10:42:15AM +0000, Shameer Kolothum Thodi wrote:
> > @@ -1552,7 +1552,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device
> > *dev, phys_addr_t orig_addr,
> > if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
> >
> > /* swiotlb pool is incorrect for this device */
> > - if (unlikely(mem->cc_shared !=
> > force_dma_unencrypted(dev)))
> > + if (unlikely(mem->cc_shared != dma_require_decrypted(dev)))
>
> Just wondering, what if a device with CC_PRIVATE set has addressing
> limitations and needs a private bounce buffer? Or is that not a use case
> at all?
Then it will correctly fail here because it is not implemented. This
protects accidently copying what should have been private data into
shared memory.
If someone ever needs this they will have to implement a swiotlb pool
for private memory along side the shared pool.
But a device that can't reach all of private wont' be able to reach
shared either, so it is basically fully broken, don't do that. The VMM
Should be setting the address layout of the VM so that the devices it
installs 'fit' within their addressing constraints. ie do not create a
VM with a 52 bit address space when your device only supports 48.
Jason
next prev parent reply other threads:[~2026-10-28 12:38 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-10 3:32 [PATCH v1 0/8] iommu/arm-smmu-v3: Support guest-level Realm VSMMU (Part-1) Nicolin Chen
2026-09-10 3:32 ` [PATCH v1 1/8] firmware: arm_rmm: Move RSI support out of arch/arm64 Nicolin Chen
2026-09-10 3:32 ` [PATCH v1 2/8] firmware: arm_rmm: Add VSMMU commands and fields Nicolin Chen
2026-10-28 9:49 ` Shameer Kolothum Thodi
2026-10-28 12:35 ` Jason Gunthorpe
2026-10-28 18:38 ` Nicolin Chen
2026-09-10 3:32 ` [PATCH v1 3/8] dma-mapping: Let a device declare that it reaches private memory Nicolin Chen
2026-09-10 3:32 ` [PATCH v1 4/8] dma-mapping: Keep DMA memory private for capable devices Nicolin Chen
2026-10-28 10:42 ` Shameer Kolothum Thodi
2026-10-28 12:38 ` Jason Gunthorpe [this message]
2026-09-10 3:32 ` [PATCH v1 5/8] iommu: Let a driver mark an IOMMU as confidential Nicolin Chen
2026-09-10 3:32 ` [PATCH v1 6/8] iommu: Introduce TDISP T=0 state for confidential IOMMUs Nicolin Chen
2026-09-17 10:48 ` sonang patel
2026-09-17 13:34 ` Jason Gunthorpe
2026-09-10 3:32 ` [PATCH v1 7/8] iommu: Park TDISP T=0 devices in the blocking domain Nicolin Chen
2026-10-28 14:19 ` Shameer Kolothum Thodi
2026-10-28 15:09 ` Jason Gunthorpe
2026-10-28 18:51 ` Nicolin Chen
2026-09-10 3:32 ` [PATCH v1 8/8] iommu/arm-smmu-v3: Probe a guest-level Realm VSMMU via RSI commands Nicolin Chen
2026-09-10 4:23 ` Nicolin Chen
2026-10-28 15:41 ` Shameer Kolothum Thodi
2026-10-28 18:08 ` Nicolin Chen
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