drm/i915: preallocate pdps for 32 bit vgpu

This is based on Mika Kuoppala's patch below:
http://article.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/61104/match=workaround+hw+preload

The patch will preallocate the page directories for 32-bit PPGTT when
i915 runs inside a virtual machine with Intel GVT-g. With this change,
the root pointers in EXECLIST context will always keep the same.

The change is needed for vGPU because Intel GVT-g will do page table
shadowing, and needs to track all the page table changes from guest
i915 driver. However, if guest PPGTT is modified through GPU commands
like LRI, it is not possible to trap the operations in the right time,
so it will be hard to make shadow PPGTT to work correctly.

Shadow PPGTT could be much simpler with this change. Meanwhile
hypervisor could simply prohibit any attempt of PPGTT modification
through GPU command for security.

The function gen8_preallocate_top_level_pdps() in the patch is from
Mika, with only one change to set "used_pdpes" to avoid duplicated
allocation later.

Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Zhiyuan Lv <zhiyuan.lv@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1441,6 +1441,33 @@ static void gen8_dump_ppgtt(struct i915_hw_ppgtt *ppgtt, struct seq_file *m)
 	}
 }
 
+static int gen8_preallocate_top_level_pdps(struct i915_hw_ppgtt *ppgtt)
+{
+	unsigned long *new_page_dirs, **new_page_tables;
+	uint32_t pdpes = I915_PDPES_PER_PDP(dev);
+	int ret;
+
+	/* We allocate temp bitmap for page tables for no gain
+	 * but as this is for init only, lets keep the things simple
+	 */
+	ret = alloc_gen8_temp_bitmaps(&new_page_dirs, &new_page_tables, pdpes);
+	if (ret)
+		return ret;
+
+	/* Allocate for all pdps regardless of how the ppgtt
+	 * was defined.
+	 */
+	ret = gen8_ppgtt_alloc_page_directories(&ppgtt->base, &ppgtt->pdp,
+						0, 1ULL << 32,
+						new_page_dirs);
+	if (!ret)
+		*ppgtt->pdp.used_pdpes = *new_page_dirs;
+
+	free_gen8_temp_bitmaps(new_page_dirs, new_page_tables, pdpes);
+
+	return ret;
+}
+
 /*
  * GEN8 legacy ppgtt programming is accomplished through a max 4 PDP registers
  * with a net effect resembling a 2-level page table in normal x86 terms. Each
@@ -1484,6 +1511,12 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 		trace_i915_page_directory_pointer_entry_alloc(&ppgtt->base,
 							      0, 0,
 							      GEN8_PML4E_SHIFT);
+
+		if (intel_vgpu_active(ppgtt->base.dev)) {
+			ret = gen8_preallocate_top_level_pdps(ppgtt);
+			if (ret)
+				goto free_scratch;
+		}
 	}
 
 	return 0;

drivers/gpu/drm/i915/intel_lrc.c

@@ -1540,7 +1540,8 @@ static int gen8_emit_bb_start(struct drm_i915_gem_request *req,
 	 * not needed in 48-bit.*/
 	if (req->ctx->ppgtt &&
 	    (intel_ring_flag(req->ring) & req->ctx->ppgtt->pd_dirty_rings)) {
-		if (!USES_FULL_48BIT_PPGTT(req->i915)) {
+		if (!USES_FULL_48BIT_PPGTT(req->i915) &&
+		    !intel_vgpu_active(req->i915->dev)) {
 			ret = intel_logical_ring_emit_pdps(req);
 			if (ret)
 				return ret;