[Intel-gfx] [PATCH v2] drm/i915: Assert we do not try to expand VMA for hugepage inside GGTT

[Chris Wilson]

We only apply the hugepage PD redirection inside the ppGTT, so during
i915_vma_insert() we want to exclude the GGTT from the additional
alignment constraints (thereby avoiding the extra GTT pressure from
fragmentation). Add an assert to document that intention alongside the
comment.

v2: After discussion with Matthew, make it a blanket GGTT ban
(previously we allowed the expansion for appgtt, and so indirectly
ggtt). There are issues we need to fix before allowing the current
appgtt to be used with hugepages, and if we do, we probably want more
care over when to expand/align, as the mappable aperture inside the ggtt
is precious.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Matthew Auld <matthew.william.auld at gmail.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Reviewed-by: Matthew Auld <matthew.william.auld at gmail.com>
---
 drivers/gpu/drm/i915/i915_vma.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index df6b63a4dfe6..d006a35cde3b 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -538,6 +538,13 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
 				rounddown_pow_of_two(vma->page_sizes.sg |
 						     I915_GTT_PAGE_SIZE_2M);
 
+			/*
+			 * Check we don't expand for the limited Global GTT
+			 * (mappable aperture is even more precious!). This
+			 * also checks that we exclude the aliasing-ppgtt.
+			 */
+			GEM_BUG_ON(i915_vma_is_ggtt(vma));
+
 			alignment = max(alignment, page_alignment);
 
 			if (vma->page_sizes.sg & I915_GTT_PAGE_SIZE_64K)
-- 
2.14.2