drm/i915/gvt: do not return error on handling force_to_nonpriv registers

Return error will cause vm hang and enter failsafe mode.
However, we don't want that happen on detecting an wrong force_to_nonpriv
register write.
Therefore, we just omit the wrong write or patch it to default value.

v2: only return 0 on detecting lri write of registers outside whitelist,
but still return error on other error conditions.  (zhenyu wang)

Signed-off-by: Zhao Yan <yan.y.zhao@intel.com>
Reviewed-by: Zhang Yulei <yulei.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -828,7 +828,8 @@ static int force_nonpriv_reg_handler(struct parser_exec_state *s,
 			data != nopid) {
 		gvt_err("Unexpected forcenonpriv 0x%x LRI write, value=0x%x\n",
 			offset, data);
-		return -EPERM;
+		patch_value(s, cmd_ptr(s, index), nopid);
+		return 0;
 	}
 	return 0;
 }

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

@@ -495,7 +495,7 @@ static int force_nonpriv_write(struct intel_vgpu *vgpu,
 		gvt_err("vgpu(%d) Invalid FORCE_NONPRIV write %x at offset %x\n",
 			vgpu->id, reg_nonpriv, offset);
 
-	return ret;
+	return 0;
 }
 
 static int ddi_buf_ctl_mmio_write(struct intel_vgpu *vgpu, unsigned int offset,