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

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Date:   Wed, 19 Jun 2019 13:29:03 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christoph Hellwig <hch@....de>,
        Potnuri Bharat Teja <bharat@...lsio.com>
Cc:     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 Mon, Jun 17, 2019 at 10:33:42AM +0200, Christoph Hellwig wrote:
> > drivers/infiniband/hw/cxgb4/qp.c
> >    129  static int alloc_host_sq(struct c4iw_rdev *rdev, struct t4_sq *sq)
> >    130  {
> >    131          sq->queue = dma_alloc_coherent(&(rdev->lldi.pdev->dev), sq->memsize,
> >    132                                         &(sq->dma_addr), GFP_KERNEL);
> >    133          if (!sq->queue)
> >    134                  return -ENOMEM;
> >    135          sq->phys_addr = virt_to_phys(sq->queue);
> >    136          dma_unmap_addr_set(sq, mapping, sq->dma_addr);
> >    137          return 0;
> >    138  }
> > 
> > Is this a bug?
> 
> 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 ?

Jason