linux-kernel - Re: next-20250627: IOMMU DMA warning during NVMe I/O completion after 06cae0e3f61c

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Message-ID: <aGPuue3_-BSPffR0@kbusch-mbp>
Date: Tue, 1 Jul 2025 10:20:41 -0400
From: Keith Busch <kbusch@...nel.org>
To: Ben Copeland <ben.copeland@...aro.org>
Cc: Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
	lkft-triage@...ts.linaro.org, regressions@...ts.linux.dev,
	linux-nvme@...ts.infradead.org,
	Dan Carpenter <dan.carpenter@...aro.org>, axboe@...nel.dk,
	sagi@...mberg.me, iommu@...ts.linux.dev
Subject: Re: next-20250627: IOMMU DMA warning during NVMe I/O completion
 after 06cae0e3f61c

On Tue, Jul 01, 2025 at 02:05:04PM +0100, Ben Copeland wrote:
> Even though SGLs are not supported, I gave you the patch a spin and
> saw the same stack traces.

Right, that patch applies only if SGL is not supported, but it's only
fixing part of the problem, so I expected it would still fail.

The dma teardown needs to be symetric to the dma mapping, but we've
removed the sg-table now, so we don't have the original mapping context
in the completion path here. Christoph replied with a patch that tries
to infer it based on the dma_addr continuity, which I think should work
for you, but I'll have to look a bit closer to be confident it's always
the correct assumption.