linux-kernel - Re: too large sg segments with commit 09324d32d2a08

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Message-ID: <20190605133002.GA13368@lst.de>
Date:   Wed, 5 Jun 2019 15:30:02 +0200
From:   Christoph Hellwig <hch@....de>
To:     Sebastian Ott <sebott@...ux.ibm.com>
Cc:     Christoph Hellwig <hch@....de>, Ming Lei <ming.lei@...hat.com>,
        Hannes Reinecke <hare@...e.com>, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: too large sg segments with commit 09324d32d2a08

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@....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@....de>
Reported-by: Sebastian Ott <sebott@...ux.ibm.com>
---
 drivers/nvme/host/pci.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index f562154551ce..524d6bd6d095 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2513,6 +2513,12 @@ static void nvme_reset_work(struct work_struct *work)
 	 */
 	dev->ctrl.max_hw_sectors = NVME_MAX_KB_SZ << 1;
 	dev->ctrl.max_segments = NVME_MAX_SEGS;
+
+	/*
+	 * Don't limit the IOMMU merged segment size.
+	 */
+	dma_set_max_seg_size(dev->dev, 0xffffffff);
+
 	mutex_unlock(&dev->shutdown_lock);

 	/*
-- 
2.20.1