On 830/845, the BLT unit invalidates the wrong PTE in its TLB after the
GATT is updated. A simple solution is then to always invalidate the TLB
of the BLT prior to each execbuffer.

This does appear to improve the stability slighty, but I am still seeing
spurious GPU deaths under memory pressure.

References: https://bugs.freedesktop.org/show_bug.cgi?id=26345
Signed-off-by: Chris Wilson <[email protected]>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c 
b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 60fc132..b825c06 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -883,6 +883,13 @@ i915_gem_execbuffer_move_to_gpu(struct intel_ring_buffer 
*ring,
        int ret;
 
        memset(&cd, 0, sizeof(cd));
+
+       /* We need to invalidate the BLT's prefetched entries after
+        * updating the GATT (as the hardware invalidates the wrong PTEs).
+        */
+       if (IS_I830(ring->dev) || IS_845G(ring->dev))
+               cd.invalidate_domains = I915_GEM_DOMAIN_RENDER;
+
        list_for_each_entry(obj, objects, exec_list)
                i915_gem_object_set_to_gpu_domain(obj, ring, &cd);
 
-- 
1.7.10

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