From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 79C0DC83001 for ; Tue, 28 Apr 2020 01:08:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 52CC1206D9 for ; Tue, 28 Apr 2020 01:08:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726333AbgD1BIJ (ORCPT ); Mon, 27 Apr 2020 21:08:09 -0400 Received: from mga05.intel.com ([192.55.52.43]:43127 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726263AbgD1BIJ (ORCPT ); Mon, 27 Apr 2020 21:08:09 -0400 IronPort-SDR: J+WjQwm+IMEz5n9R5AJqcxO0ZMhOOnogWwTOIIHi7hHZC3LI7BPg9pYO1Y+4gpXBi0XOSSaj8Y UPQPoAQVJ4zQ== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Apr 2020 18:08:08 -0700 IronPort-SDR: 2YoVZ36m76ZElHEJ97QaJ9BSnZaX0q6H1YcE2h2urZ+Ix/dX43x5tEXzq+SzYZx7OAac/BP8ym 0SsxcIBGu0dA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,325,1583222400"; d="scan'208";a="459058326" Received: from otc-nc-03.jf.intel.com (HELO otc-nc-03) ([10.54.39.25]) by fmsmga006.fm.intel.com with ESMTP; 27 Apr 2020 18:08:08 -0700 Date: Mon, 27 Apr 2020 18:08:08 -0700 From: "Raj, Ashok" To: Thomas Gleixner Cc: Fenghua Yu , Ingo Molnar , Borislav Petkov , H Peter Anvin , David Woodhouse , Lu Baolu , Dave Hansen , Tony Luck , Jacob Jun Pan , Dave Jiang , Sohil Mehta , Ravi V Shankar , linux-kernel , x86 , iommu@lists.linux-foundation.org, Ashok Raj Subject: Re: [PATCH 6/7] x86/traps: Fix up invalid PASID Message-ID: <20200428010808.GA18865@otc-nc-03> References: <1585596788-193989-1-git-send-email-fenghua.yu@intel.com> <1585596788-193989-7-git-send-email-fenghua.yu@intel.com> <87mu6ys20d.fsf@nanos.tec.linutronix.de> <20200427224646.GA103955@otc-nc-03> <874kt4pgyk.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874kt4pgyk.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thomas, On Tue, Apr 28, 2020 at 02:54:59AM +0200, Thomas Gleixner wrote: > Ashok, > > "Raj, Ashok" writes: > > On Sun, Apr 26, 2020 at 05:25:06PM +0200, Thomas Gleixner wrote: > >> Just for the record I also suggested to have a proper errorcode in the > >> #GP for ENQCMD and I surely did not suggest to avoid decoding the user > >> instructions. > > > > We certainly discussed the possiblity of adding an error code to > > identiy #GP due to ENQCMD with our HW architects. > > > > There are only a few cases that have an error code, like move to segment > > with an invalid value for instance. There were a few but i don't > > recall that entire list. > > > > Since the error code is 0 in most places, there isn't plumbing in hw to return > > this value in all cases. It appeared that due to some uarch reasons it > > wasn't as simple as it appears to /me sw kinds :-) > > Sigh. > > > So after some internal discussion we decided to take the current > > approach. Its possible that if the #GP was due to some other reason > > we might #GP another time. Since this wasn't perf or speed path we took > > this lazy approach. > > I know that the HW people's mantra is that everything can be fixed in > software and therefore slapping new features into the CPUs can be done > without thinking about the consequeses. > > But we all know from painful experience that this is fundamentally wrong > unless there is a really compelling reason. :-)... I'm still looking for the quote from Linus about RAS before he went to behavior school. > > For new features there is absolutely no reason at all. > > Can HW people pretty please understand that hardware and software have > to be co-designed and not dictated by 'some uarch reasons'. This is > nothing fundamentally new. This problem existed 30+ years ago, is well > documented and has been ignored forever. I'm tired of that, really. > > But as this seems to be unsolvable for the problem at hand can you > please document the inability, unwillingness or whatever in the > changelog? Most certainly! > > The question why this brand new_ ENQCMD + invalid PASID induced #GP does > not generate an useful error code and needs heuristics to be dealt with > is pretty obvious. > Cheers, Ashok