[PATCH 2/3] drm/i915: Assign I915_COLOR_UNEVICTABLE to the address space head_node

[Chris Wilson]

The drm_mm range manager (within i915_address_space) uses a special
drm_mm_node that excludes the unavailable range (beyond the end of the
drm_mm). However, we play games with the global GTT to use the head_node
to exclude the tail page but tell ourselves that the whole range is
available. This causes an issue when we try to evict using the full
range of the global GTT which is wider than the drm_mm, resulting in
complete confusion and castrophe. One way to resolve this would be to
use a reserved node to exclude the guard page, or we can treat the
drm_mm's head_node as our guard page and assign it the appropriate
colour.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 9bed5e9ee31b..75cd2a56b8b4 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -2160,10 +2160,14 @@ static void i915_address_space_init(struct i915_address_space *vm,
 				    const char *name)
 {
 	i915_gem_timeline_init(dev_priv, &vm->timeline, name);
+
 	drm_mm_init(&vm->mm, vm->start, vm->total);
+	vm->mm.head_node.color = I915_COLOR_UNEVICTABLE;
+
 	INIT_LIST_HEAD(&vm->active_list);
 	INIT_LIST_HEAD(&vm->inactive_list);
 	INIT_LIST_HEAD(&vm->unbound_list);
+
 	list_add_tail(&vm->global_link, &dev_priv->vm_list);
 }
 
-- 
2.11.0