[PATCH 3/4] drm/i915/gt: Always poison the kernel_context image before unparking

[Chris Wilson]

Keep scrubbing the kernel_context image with poison before we reset it
in order to demonstrate that we will be resilient in the case where it
is accidentally overwritten on idle.

Suggested-by: Imre Deak <imre.deak at intel.com>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_context_types.h |  2 ++
 drivers/gpu/drm/i915/gt/intel_engine_pm.c     | 14 ++++++++++++++
 drivers/gpu/drm/i915/gt/intel_lrc.c           |  4 ++--
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
index 9527a659546c..ca1420fb8b53 100644
--- a/drivers/gpu/drm/i915/gt/intel_context_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
@@ -17,6 +17,8 @@
 #include "intel_engine_types.h"
 #include "intel_sseu.h"
 
+#define CONTEXT_REDZONE POISON_INUSE
+
 struct i915_gem_context;
 struct i915_vma;
 struct intel_context;
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
index b9444ce29a3a..fbd44434e79d 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
@@ -35,6 +35,20 @@ static int __engine_unpark(struct intel_wakeref *wf)
 	if (!IS_ERR_OR_NULL(map))
 		engine->pinned_default_state = map;
 
+	/* Poison the kernel_context image to verify we never fully trust it */
+	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) &&
+	    engine->kernel_context->state) {
+		struct drm_i915_gem_object *obj =
+			engine->kernel_context->state->obj;
+
+		map = i915_gem_object_pin_map(obj, i915_coherent_map_type(engine->i915));
+		if (!IS_ERR(map)) {
+			memset(map, CONTEXT_REDZONE, obj->base.size);
+			i915_gem_object_flush_map(obj);
+			i915_gem_object_unpin_map(obj);
+		}
+	}
+
 	/* Discard stale context state from across idling */
 	ce = engine->kernel_context;
 	if (ce)
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 2eeb95c61a48..50e232eb8784 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -2399,7 +2399,7 @@ set_redzone(void *vaddr, const struct intel_engine_cs *engine)
 
 	vaddr += engine->context_size;
 
-	memset(vaddr, POISON_INUSE, I915_GTT_PAGE_SIZE);
+	memset(vaddr, CONTEXT_REDZONE, I915_GTT_PAGE_SIZE);
 }
 
 static void
@@ -2410,7 +2410,7 @@ check_redzone(const void *vaddr, const struct intel_engine_cs *engine)
 
 	vaddr += engine->context_size;
 
-	if (memchr_inv(vaddr, POISON_INUSE, I915_GTT_PAGE_SIZE))
+	if (memchr_inv(vaddr, CONTEXT_REDZONE, I915_GTT_PAGE_SIZE))
 		dev_err_once(engine->i915->drm.dev,
 			     "%s context redzone overwritten!\n",
 			     engine->name);
-- 
2.24.1