linux-kernel - Re: use exact allocation for dma coherent memory

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Message-ID: <20190620105124.GA25233@lst.de>
Date:   Thu, 20 Jun 2019 12:51:24 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Christoph Hellwig <hch@....de>,
        Potnuri Bharat Teja <bharat@...lsio.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Ian Abbott <abbotti@....co.uk>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>,
        devel@...verdev.osuosl.org, linux-s390@...r.kernel.org,
        Intel Linux Wireless <linuxwifi@...el.com>,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        "moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
        linux-media@...r.kernel.org
Subject: Re: use exact allocation for dma coherent memory

On Wed, Jun 19, 2019 at 01:29:03PM -0300, Jason Gunthorpe wrote:
> > Yes.  This will blow up badly on many platforms, as sq->queue
> > might be vmapped, ioremapped, come from a pool without page backing.
> 
> Gah, this addr gets fed into io_remap_pfn_range/remap_pfn_range too..
> 
> Potnuri, you should fix this.. 
> 
> You probably need to use dma_mmap_from_dev_coherent() in the mmap ?

The function to use is dma_mmap_coherent, dma_mmap_from_dev_coherent is
just an internal helper.

That beiŋ said the drivers/infiniband code has a lot of
*remap_pfn_range, and a lot of them look like they might be for
DMA memory.