Re: [igt-dev] [PATCH i-g-t] tests/i915: Add test for unaligned detiler fences

[Imre Deak <imre.deak@intel.com>]

On Mon, Jan 13, 2020 at 05:50:09PM +0000, Chris Wilson wrote:
> Quoting Imre Deak (2020-01-13 17:21:20)
> > Add a test to check the detiling on a buffer with a size that isn't
> > aligned to the detiler fence stride we add for the buffer. While writes
> > beyond the last full tile row may target an address beyond the buffer's
> > size, we still expect that such writes will not lead to a corruption
> > on memory pages that are not owned by the process performing the write.
> > 
> > The reason for this test: on TGL such writes lead to random memory
> > corruption in memory not belonging to the process. This should be
> > prevented ensuring that we keep pages that user space can access
> > (padding the object size to be tile-row size aligned) reserved in the
> > GTT address space until userspace can write through the fenced region.
> 
> This is going through a different IP block and driver paths than the
> original bug. When we are using a fence, we create a vma that is
> sufficient to include the last tile row. When we create a vma for the
> display, we don't ask for that...

Yes, then there must be some other issue too, since this test still
shows the corruption, even though it's only using a gem buffer not a
framebuffer.

> 
> --- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> @@ -344,19 +344,24 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
>  	 * put it anyway and hope that userspace can cope (but always first
>  	 * try to preserve the existing ABI).
>  	 */
> -	vma = ERR_PTR(-ENOSPC);
> -	if ((flags & PIN_MAPPABLE) == 0 &&
> -	    (!view || view->type == I915_GGTT_VIEW_NORMAL))
> -		vma = i915_gem_object_ggtt_pin(obj, view, 0, alignment,
> -					       flags |
> -					       PIN_MAPPABLE |
> -					       PIN_NONBLOCK);
> -	if (IS_ERR(vma))
> -		vma = i915_gem_object_ggtt_pin(obj, view, 0, alignment, flags);
> +	vma = i915_vma_instance(obj, &i915->ggtt.vm, view);
>  	if (IS_ERR(vma))
>  		return vma;
> 
> -	vma->display_alignment = max_t(u64, vma->display_alignment, alignment);
> +	alignment = max(vma->display_alignment, alignment);
> +
> +	ret = -ENOSPC;
> +	if ((flags & PIN_MAPPABLE) == 0 &&
> +	    vma->ggtt_view.type == I915_GGTT_VIEW_NORMAL)
> +		ret = i915_vma_pin(vma,
> +				   alignment, vma->fence_size,
> +				   flags | PIN_MAPPABLE | PIN_NONBLOCK);
> +	if (ret == -ENOSPC)
> +		ret = i915_vma_pin(vma, alignment, vma->fence_size, flags);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	vma->display_alignment = alignment;
> 
>  	i915_gem_object_flush_if_display(obj);
> 
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 17d7c525ea5c..57df22b809fa 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -619,7 +619,7 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
>  	GEM_BUG_ON(drm_mm_node_allocated(&vma->node));
> 
>  	size = max(size, vma->size);
> -	alignment = max(alignment, vma->display_alignment);
> +	alignment = max_t(typeof(alignment), alignment, vma->display_alignment);
>  	if (flags & PIN_MAPPABLE) {
>  		size = max_t(typeof(size), size, vma->fence_size);
>  		alignment = max_t(typeof(alignment),
> diff --git a/drivers/gpu/drm/i915/i915_vma_types.h b/drivers/gpu/drm/i915/i915_vma_types.h
> index e0942efd5236..2cf642ecbd7d 100644
> --- a/drivers/gpu/drm/i915/i915_vma_types.h
> +++ b/drivers/gpu/drm/i915/i915_vma_types.h
> @@ -182,7 +182,6 @@ struct i915_vma {
>  	struct i915_fence_reg *fence;
> 
>  	u64 size;
> -	u64 display_alignment;
>  	struct i915_page_sizes page_sizes;
> 
>  	/* mmap-offset associated with fencing for this vma */
> @@ -190,6 +189,7 @@ struct i915_vma {
> 
>  	u32 fence_size;
>  	u32 fence_alignment;
> +	u32 display_alignment;
> 
>  	/**
>  	 * Count of the number of times this vma has been opened by different
> 
> The partial fencing interaction with HW and peeking at the pages behind
> should be covered by selftests -- as we want to peek at physical pages.
> Mostly done already.
> -Chris
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