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Date:   Wed, 5 Jun 2019 15:57:41 +0200 (CEST)
From:   Sebastian Ott <sebott@linux.ibm.com>
To:     Christoph Hellwig <hch@lst.de>
cc:     Ming Lei <ming.lei@redhat.com>, Hannes Reinecke <hare@suse.com>,
        Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: too large sg segments with commit 09324d32d2a08
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On Wed, 5 Jun 2019, Christoph Hellwig wrote:
> Actually, it looks like something completely general isn't
> easily doable, not without some major dma API work.  Here is what
> should fix nvme, but a few other drivers will need fixes as well:
> 
> ---
> From 745541130409bc837a3416300f529b16eded8513 Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Wed, 5 Jun 2019 14:55:26 +0200
> Subject: nvme-pci: don't limit DMA segement size
> 
> NVMe uses PRPs (or optionally unlimited SGLs) for data transfers and
> has no specific limit for a single DMA segement.  Limiting the size
> will cause problems because the block layer assumes PRP-ish devices
> using a virt boundary mask don't have a segment limit.  And while this
> is true, we also really need to tell the DMA mapping layer about it,
> otherwise dma-debug will trip over it.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reported-by: Sebastian Ott <sebott@linux.ibm.com>

Works for me. Thanks!