[Intel-gfx] [PATCH] drm/i915: Add a module option for disabling use of stolen memory

[Chris Wilson]

On Sat, Jun 11, 2016 at 06:22:00PM +0300, Jani Nikula wrote:
> On Sat, 11 Jun 2016, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > One of the first steps in triaging memory corruption on module load is
> > to disable stolen. (It helps reduce the impact of the BIOS clobbering
> > our memory since we allocate our ringbuffers and initial objects from
> > stolen, if they are clobbered we get an immediate hang and garbage on
> > screen.) Rather than requesting bug reporters patch their kernel to test
> > the theory, allow us to disable stolen through a module option.
> >
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/i915_gem_stolen.c | 5 +++++
> >  drivers/gpu/drm/i915/i915_params.c     | 6 ++++++
> >  drivers/gpu/drm/i915/i915_params.h     | 1 +
> >  3 files changed, 12 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > index e9cd82290408..bb8567b1d6a4 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > @@ -411,6 +411,11 @@ int i915_gem_init_stolen(struct drm_device *dev)
> >  	}
> >  #endif
> >  
> > +	if (!i915.enable_stolen) {
> > +		DRM_INFO("Disabling use of stolen memory at user request.\n");
> > +		return 0;
> > +	}
> > +
> >  	if (ggtt->stolen_size == 0)
> >  		return 0;
> >  
> > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> > index 573e78723fc5..511528199aec 100644
> > --- a/drivers/gpu/drm/i915/i915_params.c
> > +++ b/drivers/gpu/drm/i915/i915_params.c
> > @@ -60,6 +60,7 @@ struct i915_params i915 __read_mostly = {
> >  	.enable_dp_mst = true,
> >  	.inject_load_failure = 0,
> >  	.enable_dpcd_backlight = false,
> > +	.enable_stolen = true,
> >  };
> >  
> >  module_param_named(modeset, i915.modeset, int, 0400);
> > @@ -119,6 +120,11 @@ MODULE_PARM_DESC(enable_hangcheck,
> >  	"WARNING: Disabling this can cause system wide hangs. "
> >  	"(default: true)");
> >  
> > +module_param_named(enable_stolen, i915.enable_stolen, bool, 0400);
> 
> _unsafe, to make it clear that this is for debugging?

There shouldn't be a negative consequence, some secondary effects but
nothing that I would consider unsafe. It would be the same as tainting
the kernel because of a BIOS setting.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre