drm/i915: Use partial view in mmap fault handler

Use partial view for huge BOs (bigger than half the mappable aperture)
in fault handler so that they can be accessed withough trying to make
room for them by evicting other objects.

v2:
- Only use partial views in the case where early rejection was
  previously done.
- Account variable type changes from previous reroll.
v3:
- Add a comment about overwriting existing page entries.
  (Tvrtko Ursulin)
- Whitespace fixes.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -1635,6 +1635,7 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	struct drm_i915_gem_object *obj = to_intel_bo(vma->vm_private_data);
 	struct drm_device *dev = obj->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct i915_ggtt_view view = i915_ggtt_view_normal;
 	pgoff_t page_offset;
 	unsigned long pfn;
 	int ret = 0;
@@ -1667,8 +1668,21 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 		goto unlock;
 	}
 
-	/* Now bind it into the GTT if needed */
-	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
+	/* Use a partial view if the object is bigger than the aperture. */
+	if (obj->base.size >= dev_priv->gtt.mappable_end) {
+		static const unsigned int chunk_size = 256; // 1 MiB
+		memset(&view, 0, sizeof(view));
+		view.type = I915_GGTT_VIEW_PARTIAL;
+		view.params.partial.offset = rounddown(page_offset, chunk_size);
+		view.params.partial.size =
+			min_t(unsigned int,
+			      chunk_size,
+			      (vma->vm_end - vma->vm_start)/PAGE_SIZE -
+			      view.params.partial.offset);
+	}
+
+	/* Now pin it into the GTT if needed */
+	ret = i915_gem_object_ggtt_pin(obj, &view, 0, PIN_MAPPABLE);
 	if (ret)
 		goto unlock;
 
@@ -1681,9 +1695,28 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 		goto unpin;
 
 	/* Finally, remap it using the new GTT offset */
-	pfn = dev_priv->gtt.mappable_base + i915_gem_obj_ggtt_offset(obj);
+	pfn = dev_priv->gtt.mappable_base +
+		i915_gem_obj_ggtt_offset_view(obj, &view);
 	pfn >>= PAGE_SHIFT;
 
+	if (unlikely(view.type == I915_GGTT_VIEW_PARTIAL)) {
+		/* Overriding existing pages in partial view does not cause
+		 * us any trouble as TLBs are still valid because the fault
+		 * is due to userspace losing part of the mapping or never
+		 * having accessed it before (at this partials' range).
+		 */
+		unsigned long base = vma->vm_start +
+				     (view.params.partial.offset << PAGE_SHIFT);
+		unsigned int i;
+
+		for (i = 0; i < view.params.partial.size; i++) {
+			ret = vm_insert_pfn(vma, base + i * PAGE_SIZE, pfn + i);
+			if (ret)
+				break;
+		}
+
+		obj->fault_mappable = true;
+	} else {
 		if (!obj->fault_mappable) {
 			unsigned long size = min_t(unsigned long,
 						   vma->vm_end - vma->vm_start,
@@ -1703,8 +1736,9 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 			ret = vm_insert_pfn(vma,
 					    (unsigned long)vmf->virtual_address,
 					    pfn + page_offset);
+	}
 unpin:
-	i915_gem_object_ggtt_unpin(obj);
+	i915_gem_object_ggtt_unpin_view(obj, &view);
 unlock:
 	mutex_unlock(&dev->struct_mutex);
 out:
@@ -1897,11 +1931,6 @@ i915_gem_mmap_gtt(struct drm_file *file,
 		goto unlock;
 	}
 
-	if (obj->base.size > dev_priv->gtt.mappable_end) {
-		ret = -E2BIG;
-		goto out;
-	}
-
 	if (obj->madv != I915_MADV_WILLNEED) {
 		DRM_DEBUG("Attempting to mmap a purgeable buffer\n");
 		ret = -EFAULT;