From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759913Ab1JGLSp (ORCPT ); Fri, 7 Oct 2011 07:18:45 -0400 Received: from casper.infradead.org ([85.118.1.10]:53838 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759808Ab1JGLSo convert rfc822-to-8bit (ORCPT ); Fri, 7 Oct 2011 07:18:44 -0400 Subject: Re: [PATCH 07/12] perf_events: add LBR software filter support for Intel X86 From: Peter Zijlstra To: Stephane Eranian Cc: Andi Kleen , linux-kernel@vger.kernel.org, mingo@elte.hu, acme@redhat.com, ming.m.lin@intel.com, robert.richter@amd.com, ravitillo@lbl.gov Date: Fri, 07 Oct 2011 13:18:26 +0200 In-Reply-To: References: <1317912555-9559-1-git-send-email-eranian@google.com> <1317912555-9559-8-git-send-email-eranian@google.com> <20111006153229.GJ14482@one.firstfloor.org> <1317984122.31132.6.camel@twins> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.3- Message-ID: <1317986306.31132.10.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2011-10-07 at 12:49 +0200, Stephane Eranian wrote: > > You could still fuzz it after the cpu passed through and before the > > kernel reads the LBR. Its a narrow window, but quite feasible. > > > Yeah, depending on the depth of the LBR. But then what happens, you > decode an instruction that is not what was executed. Right, and Andi's concern is that this might cause our instruction decoder to blow up, or worse. The whole false profile thing isn't really a problem, I mean, that's what you get for poking at your own instruction stream.