From: David Laight <david.laight.linux@gmail.com>
To: David Hu <xuehaohu@google.com>
Cc: "Sumit Semwal" <sumit.semwal@linaro.org>,
"Christian König" <christian.koenig@amd.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Nicolin Chen" <nicolinc@nvidia.com>,
"Leon Romanovsky" <leon@kernel.org>,
"Kevin Tian" <kevin.tian@intel.com>,
"Ankit Agrawal" <ankita@nvidia.com>,
"Alex Williamson" <alex@shazbot.org>,
linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org,
iommu@lists.linux.dev, jmoroni@google.com, praan@google.com,
kpberry@google.com, chriscli@google.com, sashiko-bot@kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH v2] dma-buf: Split sgl into page-aligned 2G chunks
Date: Tue, 23 Jun 2026 09:44:46 +0100 [thread overview]
Message-ID: <20260623094446.4a8fc2ed@pumpkin> (raw)
In-Reply-To: <20260623015459.1153884-1-xuehaohu@google.com>
On Tue, 23 Jun 2026 01:54:59 +0000
David Hu <xuehaohu@google.com> wrote:
> Currently, `fill_sg_entry()` splits the scatterlist using `UINT_MAX`.
> This creates a non-page-aligned DMA length (`0xFFFFFFFF`) for the
> first entry, resulting in non-page-aligned DMA addresses for all
> subsequent entries.
There is a separate issue of whether this code is even needed at all.
Where can transfers over 2G (never mind 4G) actually come from.
The read, write and similar system calls limit transfers to INT_MAX
(even on 64bit) and a lot of driver code will need fixing it longer
lengths are allowed though.
io_uring better enforce the same limits.
So the transfers can come directly from userspace.
Not only that but you also need a single physically contiguous buffer.
Good luck allocating that!
Now maybe there are some peer-to-peer places where the large buffer
is device memory, but they will be unusual and probably need
special treatment anyway.
David
prev parent reply other threads:[~2026-06-23 8:44 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-21 22:21 [PATCH] dma-buf: Split sgl by largest page-aligned chunk David Hu
2026-06-21 22:34 ` sashiko-bot
2026-06-22 8:13 ` David Laight
2026-06-22 21:26 ` David Hu
2026-06-23 8:25 ` David Laight
2026-06-23 1:54 ` [PATCH v2] dma-buf: Split sgl into page-aligned 2G chunks David Hu
2026-06-23 2:08 ` sashiko-bot
2026-06-23 8:44 ` David Laight [this message]
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