[Intel-gfx] [PATCH] drm/i915: Check for get_pages instead of shmem (filp)

Ben Widawsky benjamin.widawsky at intel.com
Sat Feb 6 01:48:37 UTC 2016

This behavior of checking for a shmem backed GEM object was introduced here:
commit 4c914c0c7c787b8f730128a8cdcca9c50b0784ab
Author: Brad Volkin <bradley.d.volkin at intel.com>
Date:   Tue Feb 18 10:15:45 2014 -0800

    drm/i915: Refactor shmem pread setup

It is possible for an object to not be a shmem backed GEM object (for example
userptr objects). An example of how we hit this failure can be found through
copy_batch() in the command parser because we allocate a userptr object for the
batch which contains privileged instructions. Userptr calls
drm_gem_private_object_init() which explicitly sets the filp to none.

It is equally feasible to simply remove the check altogether. You'll probably
oops with get_pages somewhere, but that's okay IMO because this condition
should be a driver bug, and not trigger-able by userspace. On this note, the
function name could probably benefit from a change, but whatever.

NOTE: I manually retyped this from a test machine. So I haven't even compiled
this exact patch.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Kristian Høgsberg <krh at bitplanet.net>
Cc: Jordan Justen <jordan.l.justen at intel.com>
Signed-off-by: Ben Widawsky <benjamin.widawsky at intel.com>
 drivers/gpu/drm/i915/i915_gem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 66b1705..a198928 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -489,7 +489,7 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,
 	*needs_clflush = 0;
-	if (!obj->base.filp)
+	if (!obj->ops->get_pages)
 		return -EINVAL;
 	if (!(obj->base.read_domains & I915_GEM_DOMAIN_CPU)) {

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