drm/i915/gvt: more locking for ppgtt mm LRU list

When the lock was introduced in commit 72aabfb8 ("drm/i915/gvt: Add mutual
lock for ppgtt mm LRU list") one place got lost.

Fixes: 72aabfb8 ("drm/i915/gvt: Add mutual lock for ppgtt mm LRU list")
Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1580742421-25194-1-git-send-email-igor.druzhinin@citrix.com

drivers/gpu/drm/i915/gvt/gtt.c

@@ -1956,7 +1956,11 @@ void _intel_vgpu_mm_release(struct kref *mm_ref)
 
 	if (mm->type == INTEL_GVT_MM_PPGTT) {
 		list_del(&mm->ppgtt_mm.list);
+
+		mutex_lock(&mm->vgpu->gvt->gtt.ppgtt_mm_lock);
 		list_del(&mm->ppgtt_mm.lru_list);
+		mutex_unlock(&mm->vgpu->gvt->gtt.ppgtt_mm_lock);
+
 		invalidate_ppgtt_mm(mm);
 	} else {
 		vfree(mm->ggtt_mm.virtual_ggtt);