linux-kernel - Re: [Intel-gfx] drm/i915: Avoid accessing the stolen address when it is unavailable

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Message-ID: <20131024205650.GC28973@bwidawsk.net>
Date:	Thu, 24 Oct 2013 13:56:50 -0700
From:	Ben Widawsky <ben@...dawsk.net>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	Chuansheng Liu <chuansheng.liu@...el.com>,
	daniel.vetter@...ll.ch, airlied@...ux.ie,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, fei.li@...el.com
Subject: Re: [Intel-gfx] drm/i915: Avoid accessing the stolen address when it
 is unavailable

On Thu, Oct 24, 2013 at 01:17:06PM +0100, Chris Wilson wrote:
> On Fri, Oct 25, 2013 at 12:33:47AM +0800, Chuansheng Liu wrote:
> > 
> > In our platform, we hit the the stolen region initialization failure case,
> > such as below log:
> > [drm:i915_stolen_to_physical] *ERROR* conflict detected with stolen region: [0x7b000000]
> > 
> > And it causes the dev_priv->mm.stolen_base is NULL, in this case, we should
> > avoid accessing it any more.
> > 
> > Here is possible call trace:
> > intel_enable_gt_powersave -- >
> > valleyview_enable_rps -- >
> > valleyview_setup_pctx
> 
> The two create_stolen routines are no-ops in that case so all that
> happens instead is that we read VLV_PCBR. However, really if
> i915_gem_object_create_stolen_for_preallocated() fails we should abort
> loading the driver as it means we have a hardware conflict and undefined
> behaviour.
> -Chris
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre

I agree. We should start treating these things as errors since no
RPS/RC6 is essentially not what anyone wants.

For another immediate solution it seems you can demote the DRM_ERROR to
DRM_DEBUG_DRIVER, and add a check in valleyview_enable_rps for the pctx
value.

-- 
Ben Widawsky, Intel Open Source Technology Center
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