Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932367Ab2JUQz3 (ORCPT ); Sun, 21 Oct 2012 12:55:29 -0400 Received: from mail-we0-f174.google.com ([74.125.82.174]:35075 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932337Ab2JUQz2 (ORCPT ); Sun, 21 Oct 2012 12:55:28 -0400 Date: Sun, 21 Oct 2012 18:55:23 +0200 From: Ingo Molnar To: Andi Kleen Cc: Peter Zijlstra , Stephane Eranian , LKML , "mingo@elte.hu" , Arnaldo Carvalho de Melo , Jiri Olsa Subject: Re: [PATCH 2/2] perf: SNB exclusive PMU access for INST_RETIRED:PREC_DIST Message-ID: <20121021165523.GA29247@gmail.com> References: <1350658326-14715-1-git-send-email-eranian@google.com> <1350658326-14715-3-git-send-email-eranian@google.com> <1350664077.2768.32.camel@twins> <1350665152.2768.41.camel@twins> <20121019172018.GA2095@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121019172018.GA2095@tassilo.jf.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1422 Lines: 44 * Andi Kleen wrote: > > > > This isn't limited to admin, right? So the above turns into a DoS on the > > > > console. > > > > > > > Ok, so how about a WARN_ON_ONCE() instead? > > > > That should be fine I guess ;-) > > imho there is need for a generic mechanism to return an error > string to the user program without such hacks. Agreed - we could return an 'extended errno' long error return value, which in reality is a pointer to an error string (in perf_attr::error_str), and copy that string to user-space at perf syscall return time. Thus error-string aware tooling could print the error string. So PMU drivers could do something obvious like: return (long)"perf: INST_RETIRED.PREC_DIST only works in exclusive mode"; The perf syscall notices these pointers by noticing that the error code returned is outside the errno range. Old userspace will get a -EINVAL and no string copied into the error string buffer. New userspace would get the error string copied into perf_attr::error_str, plus a 'normal' -EINVAL error code. The only cost on the kernel side is to make sure all "string errors" are returned as long. Thanks, Ingo -- 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/