Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754691AbbHCRUT (ORCPT ); Mon, 3 Aug 2015 13:20:19 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:32870 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171AbbHCRUR (ORCPT ); Mon, 3 Aug 2015 13:20:17 -0400 MIME-Version: 1.0 In-Reply-To: <20150802160332.GB28860@amd> References: <001e354e9435443b1720838a111620c4eec12a61.1438356386.git.len.brown@intel.com> <20150802160332.GB28860@amd> Date: Mon, 3 Aug 2015 13:20:15 -0400 X-Google-Sender-Auth: myv6LsdDbwogrsortJPIrms9FuA Message-ID: Subject: Re: [PATCH 1/1] x86: replace RDRAND forced-reseed with simple sanity check From: Len Brown To: Pavel Machek Cc: X86 ML , Linux PM list , "linux-kernel@vger.kernel.org" , Len Brown Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1076 Lines: 25 > If we trust built-in-self-test... > why do we need to do this at all? We > should check the return value at every call, anyway... Yes, we do trust built-in-self-test. Yes, we do check for errors on on every call, not just here in boot. The sanity check at boot from the kernel allows Linux to disable the feature, preventing user-space from thrashing trying to use it. There is also a line of reasoning that if the circuit is going to fail, chances are that it will fail immediately. I have no reason to believe that the circuit will fail in the field either at run-time or at boot-time. But that line of reasoning suggests that O(1 usec) to check at boot is a prudent investment -- it is certainly a better investment per time than may of the other things Linux does. thanks, Len Brown, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/