From: Jason Gunthorpe <jgg@nvidia.com>
To: Karl Mehltretter <kmehltretter@gmail.com>,
Alistair Popple <apopple@nvidia.com>
Cc: iommu@lists.linux.dev, dri-devel@lists.freedesktop.org,
"Diederik de Haas" <diederik@cknow-tech.com>,
"Joerg Roedel" <joro@8bytes.org>, "Will Deacon" <will@kernel.org>,
"Robin Murphy" <robin.murphy@arm.com>,
"Sandy Huang" <hjc@rock-chips.com>,
"Heiko Stübner" <heiko@sntech.de>, "Andy Yan" <andyshrk@163.com>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Maxime Ripard" <mripard@kernel.org>,
"Thomas Zimmermann" <tzimmermann@suse.de>,
"David Airlie" <airlied@gmail.com>,
"Simona Vetter" <simona@ffwll.ch>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Christian König" <christian.koenig@amd.com>,
"Rob Clark" <robin.clark@oss.qualcomm.com>,
"Marek Szyprowski" <m.szyprowski@samsung.com>,
"Jianfeng Liu" <liujianfeng1994@gmail.com>,
linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
linux-rockchip@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/2] iommu: Add iommu_map_sgtable_dma()
Date: Fri, 9 Oct 2026 11:43:19 -0300 [thread overview]
Message-ID: <20261009144319.GA58900@nvidia.com> (raw)
In-Reply-To: <20261009002114.67851-2-kmehltretter@gmail.com>
On Fri, Oct 09, 2026 at 02:21:13AM +0200, Karl Mehltretter wrote:
> DMA-BUF attachments provide DMA addresses, not CPU-side pages.
> iommu_map_sgtable() needs those pages, so private-domain importers such
> as Rockchip cannot use it with strict DMABUF_DEBUG.
>
> Add an iommu-dma helper to map a live attachment into another domain by
> translating through the device's default DMA domain. Roll back target
> mappings on error. This still recovers physical addresses
> internally.
Absolutely not. You cannot recover the phys_addr's from a DMABUF
expoter by using iommu_iova_to_phys(). Christian is adamant that
drivers must not use physical addresses, and I will not agree to any
hacks like this to try to end-run around his prohibition by abusing
iommu subsystem.
NAKed-by: Jason Gunthorpe <jgg@nvidia.com>
If you want to keep the domain in the rockchip driver you have to fix
DMABUF to allow an importer to use an iommu domain safely.
It *must not* be done with a scatterlist interface, sorry, I know that
is alot of work but Alistair is going to take a serious stab at it.
Many users want this, not just rockchip. So help with the work to
allow iommufd to do this and you will get it for free.
Jason
_______________________________________________
Linux-rockchip mailing list
Linux-rockchip@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-rockchip
next prev parent reply other threads:[~2026-10-09 14:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-09 0:21 [RFC PATCH 0/2] iommu, drm/rockchip: Map private-domain imports from DMA addresses Karl Mehltretter
2026-10-09 0:21 ` [RFC PATCH 1/2] iommu: Add iommu_map_sgtable_dma() Karl Mehltretter
2026-10-09 14:43 ` Jason Gunthorpe [this message]
2026-10-09 0:21 ` [RFC PATCH 2/2] drm/rockchip: Map imported buffers from DMA addresses Karl Mehltretter
2026-10-09 13:45 ` [RFC PATCH 0/2] iommu, drm/rockchip: Map private-domain imports " Robin Murphy
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