[Intel-gfx] [PATCH 17/37] drm/i915: Track vma activity per fence.context, not per engine

[Tvrtko Ursulin]

On 29/06/2018 15:54, Tvrtko Ursulin wrote:

[snip]

>> +int i915_vma_move_to_active(struct i915_vma *vma,
>> +                struct i915_request *rq,
>> +                unsigned int flags)
>> +{
>> +    struct drm_i915_gem_object *obj = vma->obj;
>> +    struct i915_gem_active *active;
>> +
>> +    lockdep_assert_held(&rq->i915->drm.struct_mutex);
>> +    GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
>> +
>> +    active = lookup_active(vma, rq->fence.context);
> 
> Never mind the radix tree, but fence.context is u64 as well. And 
> assigned values are continuously incrementing so once >4G of contexts 
> are created and destroyed aliasing is guaranteed with the kernel 
> context, or any old one.
> 
> It is probably IGT abuse territory, but a) can we be sure it will not 
> open up some exploit, and b) can we swallow this problem ourselves?

Hm.. key the radix tree with the timeline pointer instead? 1:1 to 
fence.context, natural long, and automatic lifetime management.

Regards,

Tvrtko