netdev - Re: use exact allocation for dma coherent memory

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Message-ID: <20190617083342.GA7883@lst.de>
Date:   Mon, 17 Jun 2019 10:33:42 +0200
From:   Christoph Hellwig <hch@....de>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Christoph Hellwig <hch@....de>,
        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

> 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.