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

[Lukas Wunner <lukas@wunner.de>]

On Sat, Jun 11, 2016 at 09:21:11AM +0100, Chris Wilson 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.

Just a quick drive-by observation, intelfb_alloc() calls
i915_gem_object_create_stolen() and if I follow the call chain
in that function it seems to me that dev_priv->mm.stolen_base == 0
isn't checked anywhere, so this looks like something that might break
with i915.enable_stolen=0. But probably that's what you meant with
"secondary effects".

Best regards,

Lukas

> 
> Signed-off-by: Chris Wilson <chris@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);
> +MODULE_PARM_DESC(enable_stolen,
> +	"Enable use of memory reserved (stolen) by the BIOS for graphics. "
> +	"(default: true)");
> +
>  module_param_named_unsafe(enable_ppgtt, i915.enable_ppgtt, int, 0400);
>  MODULE_PARM_DESC(enable_ppgtt,
>  	"Override PPGTT usage. "
> diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> index 1323261a0cdd..f126decae848 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -63,6 +63,7 @@ struct i915_params {
>  	bool nuclear_pageflip;
>  	bool enable_dp_mst;
>  	bool enable_dpcd_backlight;
> +	bool enable_stolen;
>  };
>  
>  extern struct i915_params i915 __read_mostly;
> -- 
> 2.8.1
> 
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