drm/i915: Use page coloring to provide the guard page at the end of the GTT
As we now mark the reserved hole (drm_mm.head_node) with the special
UNEVICTABLE color, we can use the page coloring to avoid prefetching of
the CS beyond the end of the GTT.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170206084547.27921-3-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 9f1f3bf..850d40e 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -2718,11 +2718,16 @@ static void i915_gtt_color_adjust(const struct drm_mm_node *node,
u64 *start,
u64 *end)
{
- if (node->color != color)
+ if (node->allocated && node->color != color)
*start += I915_GTT_PAGE_SIZE;
+ /* Also leave a space between the unallocated reserved node after the
+ * GTT and any objects within the GTT, i.e. we use the color adjustment
+ * to insert a guard page to prevent prefetches crossing over the
+ * GTT boundary.
+ */
node = list_next_entry(node, node_list);
- if (node->allocated && node->color != color)
+ if (node->color != color)
*end -= I915_GTT_PAGE_SIZE;
}
@@ -3243,14 +3248,14 @@ int i915_ggtt_init_hw(struct drm_i915_private *dev_priv)
INIT_LIST_HEAD(&dev_priv->vm_list);
- /* Subtract the guard page before address space initialization to
- * shrink the range used by drm_mm.
+ /* Note that we use page colouring to enforce a guard page at the
+ * end of the address space. This is required as the CS may prefetch
+ * beyond the end of the batch buffer, across the page boundary,
+ * and beyond the end of the GTT if we do not provide a guard.
*/
mutex_lock(&dev_priv->drm.struct_mutex);
- ggtt->base.total -= I915_GTT_PAGE_SIZE;
i915_address_space_init(&ggtt->base, dev_priv, "[global]");
- ggtt->base.total += I915_GTT_PAGE_SIZE;
- if (!HAS_LLC(dev_priv))
+ if (!HAS_LLC(dev_priv) && !USES_PPGTT(dev_priv))
ggtt->base.mm.color_adjust = i915_gtt_color_adjust;
mutex_unlock(&dev_priv->drm.struct_mutex);