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From:   Rob Clark <robdclark@gmail.com>
Date:   Fri, 28 Jun 2019 05:57:26 -0700
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Subject: Re: [Freedreno] [PATCH] drm/msm: correct NULL pointer dereference in context_init
To:     Brian Masney <masneyb@onstation.org>
Cc:     Jordan Crouse <jcrouse@codeaurora.org>,
        Rob Clark <robdclark@chromium.org>,
        Sean Paul <seanpaul@chromium.org>,
        Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Douglas Anderson <dianders@chromium.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Airlie <airlied@linux.ie>,
        "Kristian H. Kristensen" <hoegsberg@google.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        freedreno <freedreno@lists.freedesktop.org>
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On Wed, Jun 26, 2019 at 7:05 PM Brian Masney <masneyb@onstation.org> wrote:
>
> Correct attempted NULL pointer dereference in context_init() when
> running without an IOMMU.
>
> Signed-off-by: Brian Masney <masneyb@onstation.org>
> Fixes: 295b22ae596c ("drm/msm: Pass the MMU domain index in struct msm_file_private")
> ---
> The no IOMMU case seems like functionality that we may want to keep
> based on this comment:
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/msm/adreno/a3xx_gpu.c#L523
> Once I get the msm8974 interconnect driver done, I'm going to look into
> what needs to be done to get the IOMMU working on the Nexus 5.
>
> Alternatively, for development purposes, maybe we could have a NOOP
> IOMMU driver that would allow us to remove these NULL checks that are
> sprinkled throughout the code. I haven't looked into this in detail.
> Thoughts?

yeah, we probably want to keep !iommu support, it is at least useful
for bringup of new (or old) devices.  But tends to bitrot a since it
isn't a case that gets tested much once iommu is in place.  Perhaps
there is a way to have a null iommu/aspace, although I'm not quite
sure how that would work..

Anyways,

Reviewed-by: Rob Clark <robdclark@gmail.com>

(I guess this can go in via drm-misc-fixes unless we get some more
fixes to justify sending msm-fixes MR..)

>
>  drivers/gpu/drm/msm/msm_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 451bd4508793..83047cb2c735 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -619,7 +619,7 @@ static int context_init(struct drm_device *dev, struct drm_file *file)
>
>         msm_submitqueue_init(dev, ctx);
>
> -       ctx->aspace = priv->gpu->aspace;
> +       ctx->aspace = priv->gpu ? priv->gpu->aspace : NULL;
>         file->driver_priv = ctx;
>
>         return 0;
> --
> 2.20.1
>
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