drm/i915/gvt: Fix GFX_MODE handling

Enter failsafe if vgpu tries to change GFX_MODE controlled by host.
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -1692,8 +1692,22 @@ static int ring_mode_mmio_write(struct intel_vgpu *vgpu, unsigned int offset,
 	bool enable_execlist;
 	int ret;
 
+	(*(u32 *)p_data) &= ~_MASKED_BIT_ENABLE(1);
+	if (IS_COFFEELAKE(vgpu->gvt->dev_priv))
+		(*(u32 *)p_data) &= ~_MASKED_BIT_ENABLE(2);
 	write_vreg(vgpu, offset, p_data, bytes);
 
+	if (data & _MASKED_BIT_ENABLE(1)) {
+		enter_failsafe_mode(vgpu, GVT_FAILSAFE_UNSUPPORTED_GUEST);
+		return 0;
+	}
+
+	if (IS_COFFEELAKE(vgpu->gvt->dev_priv) &&
+	    data & _MASKED_BIT_ENABLE(2)) {
+		enter_failsafe_mode(vgpu, GVT_FAILSAFE_UNSUPPORTED_GUEST);
+		return 0;
+	}
+
 	/* when PPGTT mode enabled, we will check if guest has called
 	 * pvinfo, if not, we will treat this guest as non-gvtg-aware
 	 * guest, and stop emulating its cfg space, mmio, gtt, etc.