drm/i915: disable platform support for vGPU huge gtt pages

Currently gvt gtt handling doesn't support huge page entries, so disable
for now.

v2: remove useless 48b PPGTT check
Suggested-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: NMatthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006145041.21673-20-matthew.auld@intel.comSigned-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006221833.32439-19-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -4822,6 +4822,15 @@ int i915_gem_init(struct drm_i915_private *dev_priv)
 
 	mutex_lock(&dev_priv->drm.struct_mutex);
 
+	/*
+	 * We need to fallback to 4K pages since gvt gtt handling doesn't
+	 * support huge page entries - we will need to check either hypervisor
+	 * mm can support huge guest page or just do emulation in gvt.
+	 */
+	if (intel_vgpu_active(dev_priv))
+		mkwrite_device_info(dev_priv)->page_sizes =
+			I915_GTT_PAGE_SIZE_4K;
+
 	dev_priv->mm.unordered_timeline = dma_fence_context_alloc(1);
 
 	if (!i915_modparams.enable_execlists) {