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

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Message-ID: <20250701155810.GE6278@unreal>
Date: Tue, 1 Jul 2025 18:58:10 +0300
From: Leon Romanovsky <leonro@...dia.com>
To: Christoph Hellwig <hch@....de>
CC: Keith Busch <kbusch@...nel.org>, 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>
Subject: Re: next-20250627: IOMMU DMA warning during NVMe I/O completion
 after 06cae0e3f61c

On Tue, Jul 01, 2025 at 03:29:36PM +0200, Christoph Hellwig wrote:
> On Mon, Jun 30, 2025 at 02:25:23PM -0600, Keith Busch wrote:
> > I think the PRP handling is broken. At the very least, handling the last
> > element is wrong if it appears at the end of the list, so I think we
> > need something like this:
> 
> Yeah.
> 
> > But even that, the PRP setup doesn't match the teardown. We're calling
> > dma_map_page() on each PRP even if consecutive PRP's came from the same
> > dma mapping segment. So even if it had been coalesced, but if the device
> > doesn't support SGLs, then it would use the prp unmap path.
> 
> Yes, that's broken, and I remember fixing it before.  A little digging
> shows that my fixes disappeared between the oct 30 version of Leon's
> dma-split branch and the latest one somewhere.

Oct, 30 belongs to RFC/first version of patches.

Thanks