From 72a7a9925e2beea09b109dffb3384c9bf920d9da Mon Sep 17 00:00:00 2001
From: Zhenyu Wang <zhenyuw@linux.intel.com>
Date: Wed, 6 May 2020 17:59:18 +0800
Subject: drm/i915/gvt: Fix kernel oops for 3-level ppgtt guest
Git-commit: 72a7a9925e2beea09b109dffb3384c9bf920d9da
Patch-mainline: v5.7-rc6
References: bsc#1152489 git-fixes

As i915 won't allocate extra PDP for current default PML4 table,
so for 3-level ppgtt guest, we would hit kernel pointer access
failure on extra PDP pointers. So this trys to bypass that now.
It won't impact real shadow PPGTT setup, so guest context still
works.

This is verified on 4.15 guest kernel with i915.enable_ppgtt=1
to force on old aliasing ppgtt behavior.

Fixes: 4f15665ccbba ("drm/i915: Add ppgtt to GVT GEM context")
Reviewed-by: Xiong Zhang <xiong.y.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200506095918.124913-1-zhenyuw@linux.intel.com
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/gvt/scheduler.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/gvt/scheduler.c
+++ b/drivers/gpu/drm/i915/gvt/scheduler.c
@@ -379,7 +379,11 @@ static void set_context_ppgtt_from_shadow(struct intel_vgpu_workload *workload,
 		for (i = 0; i < GVT_RING_CTX_NR_PDPS; i++) {
 			struct i915_page_directory * const pd =
 				i915_pd_entry(ppgtt->pd, i);
-
+			/* skip now as current i915 ppgtt alloc won't allocate
+			   top level pdp for non 4-level table, won't impact
+			   shadow ppgtt. */
+			if (!pd)
+				break;
 			px_dma(pd) = mm->ppgtt_mm.shadow_pdps[i];
 		}
 	}