From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: axboe@kernel.dk, sagi@grimberg.me, ben.copeland@linaro.org,
leon@kernel.org, linux-nvme@lists.infradead.org,
linux-block@vger.kernel.org
Subject: Re: [PATCH] nvme-pci: fix dma unmapping when using PRPs and not using the IOVA mapping
Date: Mon, 7 Jul 2025 09:13:38 -0600 [thread overview]
Message-ID: <aGvkIt-j_QNo250Y@kbusch-mbp> (raw)
In-Reply-To: <20250707125223.3022531-1-hch@lst.de>
On Mon, Jul 07, 2025 at 02:52:23PM +0200, Christoph Hellwig wrote:
> The current version of the blk_rq_dma_map support in nvme-pci tries to
> reconstruct the DMA mappings from the on the wire descriptors if they
> are needed for unmapping. While this is not the case for the direct
> mapping fast path and the IOVA path, it is needed for the non-IOVA slow
> path, e.g. when using the interconnect is not dma coherent, when using
> swiotlb bounce buffering, or a IOMMU mapping that can't coalesce.
>
> While the reconstruction is easy and works fine for the SGL path, where
> the on the wire representation maps 1:1 to DMA mappings, the code to
> reconstruct the DMA mapping ranges from PRPs can't always work, as a
> given PRP layout can come from different DMA mappings, and the current
> code doesn't even always get that right.
>
> Give up on this approach and track the actual DMA mapping when actually
> needed again.
Looks good.
Reviewed-by: Keith Busch <kbusch@kernel.org>
next prev parent reply other threads:[~2025-07-07 15:13 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-07 12:52 [PATCH] nvme-pci: fix dma unmapping when using PRPs and not using the IOVA mapping Christoph Hellwig
2025-07-07 14:29 ` Keith Busch
2025-07-07 15:01 ` Christoph Hellwig
2025-07-07 15:13 ` Keith Busch
2025-07-07 15:13 ` Keith Busch [this message]
2025-07-08 12:55 ` Jens Axboe
2025-07-11 0:25 ` Klara Modin
2025-07-11 0:37 ` Keith Busch
2025-07-11 8:32 ` Christoph Hellwig
2025-07-11 9:07 ` Klara Modin
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