netdev - Re: DPAA2 triggers, [PATCH] dma debug: report -EEXIST errors in add_dma

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Date:   Fri, 1 Oct 2021 06:19:59 +0200
From:   Christoph Hellwig <hch@....de>
To:     Ioana Ciornei <ioana.ciornei@....com>
Cc:     Jeremy Linton <jeremy.linton@....com>,
        Hamza Mahfooz <someguy@...ective-light.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: DPAA2 triggers, [PATCH] dma debug: report -EEXIST errors in
 add_dma_entry

On Tue, Sep 14, 2021 at 03:45:06PM +0000, Ioana Ciornei wrote:
> [  245.927020] fsl_dpaa2_eth dpni.3: scather-gather idx 0 P=20a7320000 N=20a7320 D=20a7320000 L=30 DMA_BIDIRECTIONAL dma map error check not applicable·
> [  245.927048] fsl_dpaa2_eth dpni.3: scather-gather idx 1 P=20a7320030 N=20a7320 D=20a7320030 L=5a8 DMA_BIDIRECTIONAL dma map error check not applicable
> [  245.927062] DMA-API: cacheline tracking EEXIST, overlapping mappings aren't supported
> 
> The first line is the dump of the dma_debug_entry which is already present
> in the radix tree and the second one is the entry which just triggered
> the EEXIST.
> 
> As we can see, they are not actually overlapping, at least from my
> understanding. The first one starts at 0x20a7320000 with a size 0x30
> and the second one at 0x20a7320030.

They overlap the cache lines.  Which means if you use this driver
on a system that is not dma coherent you will corrupt data.