Re: [PATCH v4 14/18] drm/i915: object size needs to be u64

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jul 08, 2015 at 12:22:58PM +0100, Michel Thierry wrote:
> On 7/7/2015 9:08 PM, Chris Wilson wrote:
> >On Tue, Jul 07, 2015 at 04:44:30PM +0100, Michel Thierry wrote:
> >>On 7/7/2015 4:27 PM, Chris Wilson wrote:
> >>>On Tue, Jul 07, 2015 at 04:14:59PM +0100, Michel Thierry wrote:
> >>>>In a 48b world, users can try to allocate buffers bigger than 4GB; in
> >>>>these cases it is important that size is a 64b variable.
> >>>>
> >>>>Also added a warning for illegal bind with size = 0.
> >>>>
> >>>>Signed-off-by: Michel Thierry <michel.thierry@intel.com>
> >>>>---
> >>>>  drivers/gpu/drm/i915/i915_gem.c     | 5 +++--
> >>>>  drivers/gpu/drm/i915/i915_gem_gtt.c | 3 +++
> >>>>  2 files changed, 6 insertions(+), 2 deletions(-)
> >>>>
> >>>>diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >>>>index a0bff41..ebfb789 100644
> >>>>--- a/drivers/gpu/drm/i915/i915_gem.c
> >>>>+++ b/drivers/gpu/drm/i915/i915_gem.c
> >>>>@@ -3718,7 +3718,8 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
> >>>>  {
> >>>>  	struct drm_device *dev = obj->base.dev;
> >>>>  	struct drm_i915_private *dev_priv = dev->dev_private;
> >>>>-	u32 size, fence_size, fence_alignment, unfenced_alignment;
> >>>>+	u32 fence_alignment, unfenced_alignment;
> >>>>+	u64 size, fence_size;
> >>>>  	u64 start =
> >>>>  		flags & PIN_OFFSET_BIAS ? flags & PIN_OFFSET_MASK : 0;
> >>>>  	u64 end =
> >>>>@@ -3777,7 +3778,7 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
> >>>>  	 * attempt to find space.
> >>>>  	 */
> >>>>  	if (size > end) {
> >>>>-		DRM_DEBUG("Attempting to bind an object (view type=%u) larger than the aperture: size=%u > %s aperture=%llu\n",
> >>>>+		DRM_DEBUG("Attempting to bind an object (view type=%u) larger than the aperture: size=%llu > %s aperture=%llu\n",
> >>>>  			  ggtt_view ? ggtt_view->type : 0,
> >>>>  			  size,
> >>>>  			  flags & PIN_MAPPABLE ? "mappable" : "total",
> >>>>diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> >>>>index 449a245..900bce6 100644
> >>>>--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> >>>>+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> >>>>@@ -3312,6 +3312,9 @@ int i915_vma_bind(struct i915_vma *vma, enum i915_cache_level cache_level,
> >>>>  	if (WARN_ON(flags == 0))
> >>>>  		return -EINVAL;
> >>>>
> >>>>+	if (WARN_ON(vma->node.size == 0))
> >>>>+		return -EINVAL;
> >>>
> >>>This is superfluous. We don't allow size=0 object creation, and the test
> >>>is better (if at all) at vma_create, but what you mean here is
> >>>WARN_ON(!drm_mm_node_allocated()) which seems sensisble. And both of
> >>>these would be better as ENODEV so we don't confuse the user when they
> >>>get propagated back to userspace.
> >>>-Chris
> >>>
> >>My idea was to catch the node.size overflow if the variable is
> >>inadvertently changed back to u32 (which has already happen in other
> >>places).
> >
> >Ok, that didn't come across when I just read node.size == 0 (what are
> >chances that node.size was exactly 2^32 and then truncated?)
> >
> Only a test explicitly looking for this kind of issues (I guess). In that
> test, objects bigger than 2^32 were truncated, while objects exactly 2^32
> were hitting a WARN in the driver; alloc_pages wouldn't do anything because
> node.size == 0, and then insert would complain no pages existed.
> 
> >vma->node should be fairly opaque, and if possible we want the checks in
> >drm_mm.c - if we can think of good tests for that layer.
> >
> >Certainly drm_mm_reserve_node() probably wants a few sanity checks.
> >Though most of those should fall out when it can't do the reservation
> >the user requests.
> Or change drm_mm_insert_node_in_range_generic() to warn when size==0?

WARN_ON(vma->node.size != obj->base.size) ? Feel free to get the casting
right - I suck at implicit C integer conversion rules ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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