drm/i915: Record the default hw state after reset upon load

Take a copy of the HW state after a reset upon module loading by
executing a context switch from a blank context to the kernel context,
thus saving the default hw state over the blank context image.
We can then use the default hw state to initialise any future context,
ensuring that each starts with the default view of hw state.

v2: Unmap our default state from the GTT after stealing it from the
context. This should stop us from accidentally overwriting it via the
GTT (and frees up some precious GTT space).

Testcase: igt/gem_ctx_isolation
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171110142634.10551-7-chris@chris-wilson.co.uk

1 files changed, 12 insertions, 43 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index c05c3d7d21a5..2db040695035 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -418,8 +418,8 @@ out:
 	return ctx;
 }
 
-static struct i915_gem_context *
-create_kernel_context(struct drm_i915_private *i915, int prio)
+struct i915_gem_context *
+i915_gem_context_create_kernel(struct drm_i915_private *i915, int prio)
 {
 	struct i915_gem_context *ctx;
 
@@ -473,7 +473,7 @@ int i915_gem_contexts_init(struct drm_i915_private *dev_priv)
 	ida_init(&dev_priv->contexts.hw_ida);
 
 	/* lowest priority; idle task */
-	ctx = create_kernel_context(dev_priv, I915_PRIORITY_MIN);
+	ctx = i915_gem_context_create_kernel(dev_priv, I915_PRIORITY_MIN);
 	if (IS_ERR(ctx)) {
 		DRM_ERROR("Failed to create default global context\n");
 		err = PTR_ERR(ctx);
@@ -487,7 +487,7 @@ int i915_gem_contexts_init(struct drm_i915_private *dev_priv)
 	dev_priv->kernel_context = ctx;
 
 	/* highest priority; preempting task */
-	ctx = create_kernel_context(dev_priv, INT_MAX);
+	ctx = i915_gem_context_create_kernel(dev_priv, INT_MAX);
 	if (IS_ERR(ctx)) {
 		DRM_ERROR("Failed to create default preempt context\n");
 		err = PTR_ERR(ctx);
@@ -522,28 +522,6 @@ void i915_gem_contexts_lost(struct drm_i915_private *dev_priv)
 		engine->context_unpin(engine, engine->last_retired_context);
 		engine->last_retired_context = NULL;
 	}
-
-	/* Force the GPU state to be restored on enabling */
-	if (!i915_modparams.enable_execlists) {
-		struct i915_gem_context *ctx;
-
-		list_for_each_entry(ctx, &dev_priv->contexts.list, link) {
-			if (!i915_gem_context_is_default(ctx))
-				continue;
-
-			for_each_engine(engine, dev_priv, id)
-				ctx->engine[engine->id].initialised = false;
-
-			ctx->remap_slice = ALL_L3_SLICES(dev_priv);
-		}
-
-		for_each_engine(engine, dev_priv, id) {
-			struct intel_context *kce =
-				&dev_priv->kernel_context->engine[engine->id];
-
-			kce->initialised = true;
-		}
-	}
 }
 
 void i915_gem_contexts_fini(struct drm_i915_private *i915)
@@ -718,9 +696,6 @@ static inline bool skip_rcs_switch(struct i915_hw_ppgtt *ppgtt,
 	if (to->remap_slice)
 		return false;
 
-	if (!to->engine[RCS].initialised)
-		return false;
-
 	if (ppgtt && (intel_engine_flag(engine) & ppgtt->pd_dirty_rings))
 		return false;
 
@@ -795,11 +770,14 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 			return ret;
 	}
 
-	if (!to->engine[RCS].initialised || i915_gem_context_is_default(to))
-		/* NB: If we inhibit the restore, the context is not allowed to
-		 * die because future work may end up depending on valid address
-		 * space. This means we must enforce that a page table load
-		 * occur when this occurs. */
+	if (i915_gem_context_is_kernel(to))
+		/*
+		 * The kernel context(s) is treated as pure scratch and is not
+		 * expected to retain any state (as we sacrifice it during
+		 * suspend and on resume it may be corrupted). This is ok,
+		 * as nothing actually executes using the kernel context; it
+		 * is purely used for flushing user contexts.
+		 */
 		hw_flags = MI_RESTORE_INHIBIT;
 	else if (ppgtt && intel_engine_flag(engine) & ppgtt->pd_dirty_rings)
 		hw_flags = MI_FORCE_RESTORE;
@@ -843,15 +821,6 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 		to->remap_slice &= ~(1<<i);
 	}
 
-	if (!to->engine[RCS].initialised) {
-		if (engine->init_context) {
-			ret = engine->init_context(req);
-			if (ret)
-				return ret;
-		}
-		to->engine[RCS].initialised = true;
-	}
-
 	return 0;
 }