drm/i915: Support replaying GPU hangs with captured context image

When debugging GPU hangs Mesa developers are finding it useful to replay
the captured error state against the simulator. But due various simulator
limitations which prevent replicating all hangs, one step further is being
able to replay against a real GPU.

This is almost doable today with the missing part being able to upload the
captured context image into the driver state prior to executing the
uploaded hanging batch and all the buffers.

To enable this last part we add a new context parameter called
I915_CONTEXT_PARAM_CONTEXT_IMAGE. It follows the existing SSEU
configuration pattern of being able to select which context to apply
against, paired with the actual image and its size.

Since this is adding a new concept of debug only uapi, we hide it behind
a new kconfig option and also require activation with a module parameter.
Together with a warning banner printed at driver load, all those combined
should be sufficient to guard against inadvertently enabling the feature.

In terms of implementation we allow the legacy context set param to be
used since that removes the need to record the per context data in the
proto context, while still allowing flexibility of specifying context
images for any context.

Mesa MR using the uapi can be seen at:
  https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27594

v2:
 * Fix whitespace alignment as per checkpatch.
 * Added warning on userspace misuse.
 * Rebase for extracting ce->default_state shadowing.

v3:
 * Rebase for I915_CONTEXT_PARAM_LOW_LATENCY.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Carlos Santa <carlos.santa@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Tested-by: Carlos Santa <carlos.santa@intel.com>
Signed-off-by: Tvrtko Ursulin <tursulin@igalia.com>
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20240514145939.87427-2-tursulin@igalia.com

1 files changed, 27 insertions, 0 deletions

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index d4d86e566e07..535cb68fdb5c 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -2163,6 +2163,15 @@ struct drm_i915_gem_context_param {
  * supports this per context flag.
  */
 #define I915_CONTEXT_PARAM_LOW_LATENCY		0xe
+
+/*
+ * I915_CONTEXT_PARAM_CONTEXT_IMAGE:
+ *
+ * Allows userspace to provide own context images.
+ *
+ * Note that this is a debug API not available on production kernel builds.
+ */
+#define I915_CONTEXT_PARAM_CONTEXT_IMAGE	0xf
 /* Must be kept compact -- no holes and well documented */
 
 	/** @value: Context parameter value to be set or queried */
@@ -2564,6 +2573,24 @@ struct i915_context_param_engines {
 	struct i915_engine_class_instance engines[N__]; \
 } __attribute__((packed)) name__
 
+struct i915_gem_context_param_context_image {
+	/** @engine: Engine class & instance to be configured. */
+	struct i915_engine_class_instance engine;
+
+	/** @flags: One of the supported flags or zero. */
+	__u32 flags;
+#define I915_CONTEXT_IMAGE_FLAG_ENGINE_INDEX (1u << 0)
+
+	/** @size: Size of the image blob pointed to by @image. */
+	__u32 size;
+
+	/** @mbz: Must be zero. */
+	__u32 mbz;
+
+	/** @image: Userspace memory containing the context image. */
+	__u64 image;
+} __attribute__((packed));
+
 /**
  * struct drm_i915_gem_context_create_ext_setparam - Context parameter
  * to set or query during context creation.