drm/i915/gvt: set the correct default value of CTX STATUS PTR

commit a34f8363 upstream.

Fix wrong initial csb read pointer value. This fixes the random
engine timeout issue in guest when guest boots up.

Fixes: 8453d674 ("drm/i915/gvt: vGPU execlist virtualization")
Signed-off-by: Min He <min.he@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -778,7 +778,8 @@ static void init_vgpu_execlist(struct intel_vgpu *vgpu, int ring_id)
 			_EL_OFFSET_STATUS_PTR);
 
 	ctx_status_ptr.dw = vgpu_vreg(vgpu, ctx_status_ptr_reg);
-	ctx_status_ptr.read_ptr = ctx_status_ptr.write_ptr = 0x7;
+	ctx_status_ptr.read_ptr = 0;
+	ctx_status_ptr.write_ptr = 0x7;
 	vgpu_vreg(vgpu, ctx_status_ptr_reg) = ctx_status_ptr.dw;
 }