Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751760AbdGBN6C (ORCPT ); Sun, 2 Jul 2017 09:58:02 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:39706 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750818AbdGBN6B (ORCPT ); Sun, 2 Jul 2017 09:58:01 -0400 Date: Sun, 2 Jul 2017 15:57:50 +0200 (CEST) From: Thomas Gleixner To: Vikas Shivappa cc: x86@kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com, peterz@infradead.org, ravi.v.shankar@intel.com, vikas.shivappa@intel.com, tony.luck@intel.com, fenghua.yu@intel.com, andi.kleen@intel.com Subject: Re: [PATCH 21/21] x86/intel_rdt/mbm: Handle counter overflow In-Reply-To: <1498503368-20173-22-git-send-email-vikas.shivappa@linux.intel.com> Message-ID: References: <1498503368-20173-1-git-send-email-vikas.shivappa@linux.intel.com> <1498503368-20173-22-git-send-email-vikas.shivappa@linux.intel.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 793 Lines: 26 On Mon, 26 Jun 2017, Vikas Shivappa wrote: > +static void mbm_update(struct rdt_domain *d, int rmid) > +{ > + struct rmid_read rr; > + > + rr.first = false; > + rr.d = d; > + > + if (is_mbm_total_enabled()) { > + rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID; > + __mon_event_count(rmid, &rr); This is broken as it is not protected against a concurrent read from user space which comes in via a smp function call. This means both the internal state and __rmid_read() are unprotected. I'm not sure whether it's enough to disable interrupts around __mon_event_count(), but that's the minimal protection required. It's definitely good enough for __rmid_read(), but it might not be sufficient for protecting domain->mbm_[local|total]. I leave the exercise of figuring that out to you. Thanks, tglx