linux-kernel - Re: [PATCH v6 00/16] dma-mapping: migrate to physical address-based API

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Message-ID: <aNLnXwAJveHIqfz0@kbusch-mbp>
Date: Tue, 23 Sep 2025 12:30:55 -0600
From: Keith Busch <kbusch@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Leon Romanovsky <leon@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Abdiel Janulgue <abdiel.janulgue@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, Danilo Krummrich <dakr@...nel.org>,
	David Hildenbrand <david@...hat.com>, iommu@...ts.linux.dev,
	Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Joerg Roedel <joro@...tes.org>, Jonathan Corbet <corbet@....net>,
	Juergen Gross <jgross@...e.com>, kasan-dev@...glegroups.com,
	linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-nvme@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	linux-trace-kernel@...r.kernel.org,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Robin Murphy <robin.murphy@....com>, rust-for-linux@...r.kernel.org,
	Sagi Grimberg <sagi@...mberg.me>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	virtualization@...ts.linux.dev, Will Deacon <will@...nel.org>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v6 00/16] dma-mapping: migrate to physical address-based
 API

On Tue, Sep 23, 2025 at 02:09:36PM -0300, Jason Gunthorpe wrote:
> On Sat, Sep 20, 2025 at 06:47:27PM -0600, Keith Busch wrote:
> > 
> > One other thing to note, this was runing on arm64 platform using smmu
> > configured with 64k pages. If your iommu granule is 4k instead, we
> > wouldn't use the blk_dma_map_direct path.
> 
> I spent some time looking to see if I could guess what this is and
> came up empty. It seems most likely we are leaking a dma mapping
> tracking somehow? The DMA API side is pretty simple here though..

Yeah, nothing stood out to me here either.
 
> Not sure the 64k/4k itself is a cause, but triggering the non-iova
> flow is probably the issue.
> 
> Can you check the output of this debugfs:

I don't have a system in this state at the moment, so we checked
previous logs on machines running older kernels. It's extermely
uncommon, but this error was happening prior to this series, so I don't
think this introduced any new problem here. I'll keeping looking, but I
don't think we'll make much progress if I can't find a more reliable
reproducer.

Thanks!