Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752678AbaJUEMN (ORCPT ); Tue, 21 Oct 2014 00:12:13 -0400 Received: from fbr04.mfg.siteprotect.com ([64.26.60.139]:39199 "EHLO fbr04.mfg.siteprotect.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750750AbaJUEML (ORCPT ); Tue, 21 Oct 2014 00:12:11 -0400 X-Greylist: delayed 337 seconds by postgrey-1.27 at vger.kernel.org; Tue, 21 Oct 2014 00:12:11 EDT Date: Tue, 21 Oct 2014 00:06:54 -0400 (EDT) From: Vince Weaver X-X-Sender: vince@pianoman.cluster.toy To: Andy Lutomirski cc: Peter Zijlstra , Valdis Kletnieks , "linux-kernel@vger.kernel.org" , Paul Mackerras , Arnaldo Carvalho de Melo , Ingo Molnar , Kees Cook , Andrea Arcangeli , Erik Bosman Subject: Re: [RFC 0/5] CR4 handling improvements In-Reply-To: Message-ID: References: User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-CTCH-Spam: Unknown X-CTCH-RefID: str=0001.0A020205.5445DBC9.01D3,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 14 Oct 2014, Andy Lutomirski wrote: > This little series tightens up rdpmc permissions. With it applied, > rdpmc can only be used if a perf_event is actually mmapped. For now, > this is only really useful for seccomp. So just to be difficult... I am aware of at least one group who is doing low-latency performance measures using rdpmc on Linux. They start the counters manually by poking the MSRs directly (bypassing perf_event_open()). They use rdpmc, grateful for the fact that currently CR4 is set up so they can do this w/o patching the kernel. These patches of course would break this use case... Vince -- 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/