drm/i915/execlists: Request the kernel context be pinned high

PIN_HIGH is an expensive operation (in comparison to allocating from the
hole stack) unsuitable for frequent use (such as switching between
contexts). However, the kernel context should be pinned just once for
the lifetime of the driver, and here it is appropriate to keep it out of
the mappable range (in order to maximise mappable space for users).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161218153724.8439-6-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_lrc.c

@@ -767,6 +767,7 @@ static int execlists_context_pin(struct intel_engine_cs *engine,
 				 struct i915_gem_context *ctx)
 {
 	struct intel_context *ce = &ctx->engine[engine->id];
+	unsigned int flags;
 	void *vaddr;
 	int ret;
 
@@ -781,8 +782,11 @@ static int execlists_context_pin(struct intel_engine_cs *engine,
 			goto err;
 	}
 
-	ret = i915_vma_pin(ce->state, 0, GEN8_LR_CONTEXT_ALIGN,
-			   PIN_OFFSET_BIAS | GUC_WOPCM_TOP | PIN_GLOBAL);
+	flags = PIN_OFFSET_BIAS | GUC_WOPCM_TOP | PIN_GLOBAL;
+	if (ctx == ctx->i915->kernel_context)
+		flags |= PIN_HIGH;
+
+	ret = i915_vma_pin(ce->state, 0, GEN8_LR_CONTEXT_ALIGN, flags);
 	if (ret)
 		goto err;