[Intel-gfx] [PATCH] drm/i915: Quietly reject attempts to create non-pagealigned stolen objects

[Daniel Vetter]

On Wed, Dec 10, 2014 at 08:17:11AM +0000, Chris Wilson wrote:
> This added as a BUG_ON as it considered that no one would ever request
> an unaligned object. However, it turns out that some BIOSes will
> allocate a scanout that is offset from 0 and not aligned to a page
> boundary, and we were passing this through and hitting the BUG_ON during
> boot.
> 
> Quietly reject such a request to reserve the unaligned stolen object and
> let the boot continue, restoring previous behaviour (i.e. no BIOS
> framebuffer preservation).
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86883
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: stable at vger.kernel.org
> ---
>  drivers/gpu/drm/i915/i915_gem_stolen.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index 5c616ec2c5c8..a3bc0fa07c6c 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -646,13 +646,15 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
>  	DRM_DEBUG_KMS("creating preallocated stolen object: stolen_offset=%x, gtt_offset=%x, size=%x\n",
>  			stolen_offset, gtt_offset, size);
>  
> -	/* KISS and expect everything to be page-aligned */
> -	BUG_ON(stolen_offset & 4095);
> -	BUG_ON(size & 4095);
> -
>  	if (WARN_ON(size == 0))
>  		return NULL;
>  
> +	/* KISS and expect everything to be GTT page-aligned */
> +	if ((stolen_offset | size) & 4095) {

Imo we should stil WARN_ON and fixup up the takeover code to align things
properly ...
-Daniel

> +		DRM_DEBUG_KMS("request for unaligned stolen object, denied\n");
> +		return NULL;
> +	}
> +
>  	stolen = kzalloc(sizeof(*stolen), GFP_KERNEL);
>  	if (!stolen)
>  		return NULL;
> -- 
> 2.1.3
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch