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

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Message-ID: <aGaTw7SzermpfiD7@kbusch-mbp>
Date: Thu, 3 Jul 2025 08:29:23 -0600
From: Keith Busch <kbusch@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Ben Copeland <ben.copeland@...aro.org>, 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,
	Leon Romanovsky <leonro@...dia.com>
Subject: Re: next-20250627: IOMMU DMA warning during NVMe I/O completion
 after 06cae0e3f61c

On Thu, Jul 03, 2025 at 11:30:42AM +0200, Christoph Hellwig wrote:
> I think the idea to reconstruct the dma addresses from PRPs should
> be considered a failure by now.  It works fine for SGLs, but for
> PRPs we're better off just stashing them away.  Bob, can you try

s/Bob/Ben

> something like the patch below?  To be fully safe it needs a mempool,
> and it could use some cleanups, but it does pass testing on my setup
> here, so I'd love to see if if fixes your issue.

Thanks for confirming.

While this is starting to look a bit messy, I believe it's still an
overall win: you've cut down the vector walking in the setup path from 3
to 1, which reduces a non-trivial amount of overhead for even moderately
sized IO.