[Intel-gfx] [PATCH 2/2] drm/i915: Don't access snooped pages through the GTT (even for error capture)

[Chris Wilson]

We want to use the GTT for reading back objects upon an error so that we
have exactly the information that the GPU saw. However, it is verboten
to access snoopable pages through the GTT and causes my PineView GPU to
throw a page fault instead.

This has not been a problem in the past as we only dumped ringbuffers
and batchbuffers, both of which must be uncached. However, the
introduction of HWS page dumping leads to a read of a snooped object
through the GTT. This was introduced by

commit f3ce3821393e31a3f1a8ca6c24eb2d735a428445
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Thu Jan 23 22:40:36 2014 +0000

    drm/i915: Include HW status page in error capture

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gpu_error.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 6d5ab945132c..3b18c2dff3b8 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -527,7 +527,8 @@ i915_error_object_create_sized(struct drm_i915_private *dev_priv,
 			goto unwind;
 
 		local_irq_save(flags);
-		if (reloc_offset < dev_priv->gtt.mappable_end &&
+		if (src->cache_level == I915_CACHE_NONE &&
+		    reloc_offset < dev_priv->gtt.mappable_end &&
 		    src->has_global_gtt_mapping &&
 		    i915_is_ggtt(vm)) {
 			void __iomem *s;
-- 
1.9.rc1