[PATCH] drm/i915: Don't oops in dumb_create ioctl if we have no crtcs

[PATCH] drm/i915: Don't oops in dumb_create ioctl if we have no crtcs

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

Make sure we have a crtc before probing its primary plane's
max stride. Initially I thought we can't get this far without
crtcs, but looks like we can via the dumb_create ioctl.

Not sure if we shouldn't disable dumb buffer support entirely
when we have no crtcs, but that would require some amount of work
as the only thing currently being checked is dev->driver->dumb_create
which we'd have to convert to some device specific dynamic thing.

Cc: stable@vger.kernel.org
Reported-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Fixes: aa5ca8b7421c ("drm/i915: Align dumb buffer stride to 4k to allow for gtt remapping")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 1f93860fb897..331030765ca9 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -2543,6 +2543,9 @@ u32 intel_plane_fb_max_stride(struct drm_i915_private *dev_priv,
 	 * the highest stride limits of them all.
 	 */
 	crtc = intel_get_crtc_for_pipe(dev_priv, PIPE_A);
+	if (!crtc)
+		return 0;
+
 	plane = to_intel_plane(crtc->base.primary);
 
 	return plane->max_stride(plane, pixel_format, modifier,
-- 
2.23.0

Re: [Intel-gfx] [PATCH] drm/i915: Don't oops in dumb_create ioctl if we have no crtcs

[Chris Wilson]

Quoting Ville Syrjala (2019-11-06 17:23:49)
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Make sure we have a crtc before probing its primary plane's
> max stride. Initially I thought we can't get this far without
> crtcs, but looks like we can via the dumb_create ioctl.
> 
> Not sure if we shouldn't disable dumb buffer support entirely
> when we have no crtcs, but that would require some amount of work
> as the only thing currently being checked is dev->driver->dumb_create
> which we'd have to convert to some device specific dynamic thing.
> 
> Cc: stable@vger.kernel.org
> Reported-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Fixes: aa5ca8b7421c ("drm/i915: Align dumb buffer stride to 4k to allow for gtt remapping")
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 1f93860fb897..331030765ca9 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -2543,6 +2543,9 @@ u32 intel_plane_fb_max_stride(struct drm_i915_private *dev_priv,
>          * the highest stride limits of them all.
>          */
>         crtc = intel_get_crtc_for_pipe(dev_priv, PIPE_A);
> +       if (!crtc)
> +               return 0;
> +

Callers:
intel_fb_max_stride -> intel_framebuffer_init, not used if no display
intel_fb_stride_alignment,
	0 -> intel_tile_size() alignment. ok ->
	intel_framebuffer_init, not used as no display

-> i915_gem_dumb_create -> args->pitch = PAGE_ALIGN()

Ok, not as horrible as I feared when I saw return 0 from max_stride!

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris