[Intel-gfx] [PATCH 1/3] drm/i915: Flush the context object from the CPU caches upon switching

[Chris Wilson]

The issue is that we stale data in the CPU caches, when we come to
swap-out the object, the CPU may short-circuit the reads from those
cacheline and so corrupt the context object.

Secondary, leaving the context object as being marked in the CPU write
domain whilst on the GPU active list is a bad idea and will throw
warnings later.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_context.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 9ae3f2c..fd978bb 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -374,6 +374,13 @@ static int do_switch(struct drm_i915_gem_object *from_obj,
 	if (ret)
 		return ret;
 
+	/* Clear this page out of any CPU caches for coherent swap-in/out */
+	ret = i915_gem_object_set_to_gtt_domain(to->obj, false);
+	if (ret) {
+		i915_gem_object_unpin(to->obj);
+		return ret;
+	}
+
 	if (!to->obj->has_global_gtt_mapping)
 		i915_gem_gtt_bind_object(to->obj, to->obj->cache_level);
 
-- 
1.7.10.4