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,USER_AGENT_MUTT autolearn=ham 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 2E29BC31E45 for ; Fri, 14 Jun 2019 01:15:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 012D820B7C for ; Fri, 14 Jun 2019 01:15:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726581AbfFNBPP (ORCPT ); Thu, 13 Jun 2019 21:15:15 -0400 Received: from mga06.intel.com ([134.134.136.31]:15131 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725616AbfFNBPO (ORCPT ); Thu, 13 Jun 2019 21:15:14 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Jun 2019 18:15:14 -0700 X-ExtLoop1: 1 Received: from ranerica-svr.sc.intel.com ([172.25.110.23]) by orsmga005.jf.intel.com with ESMTP; 13 Jun 2019 18:15:13 -0700 Date: Thu, 13 Jun 2019 18:14:54 -0700 From: Ricardo Neri To: Thomas Gleixner Cc: Ingo Molnar , Borislav Petkov , Ashok Raj , Joerg Roedel , Andi Kleen , Peter Zijlstra , Suravee Suthikulpanit , Stephane Eranian , "Ravi V. Shankar" , Randy Dunlap , x86@kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Ricardo Neri , "H. Peter Anvin" , Tony Luck , Clemens Ladisch , Arnd Bergmann , Philippe Ombredanne , Kate Stewart , "Rafael J. Wysocki" Subject: Re: [RFC PATCH v4 05/21] x86/hpet: Reserve timer for the HPET hardlockup detector Message-ID: <20190614011454.GA6347@ranerica-svr.sc.intel.com> References: <1558660583-28561-1-git-send-email-ricardo.neri-calderon@linux.intel.com> <1558660583-28561-6-git-send-email-ricardo.neri-calderon@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 11, 2019 at 09:54:25PM +0200, Thomas Gleixner wrote: > On Thu, 23 May 2019, Ricardo Neri wrote: > > > HPET timer 2 will be used to drive the HPET-based hardlockup detector. > > Reserve such timer to ensure it cannot be used by user space programs or > > for clock events. > > > > When looking for MSI-capable timers for clock events, skip timer 2 if > > the HPET hardlockup detector is selected. > > Why? Both the changelog and the code change lack an explanation why this > timer is actually touched after it got reserved for the platform. The > reservation should make it inaccessible for other things. hpet_reserve_platform_timers() will give the HPET char driver a data structure which specifies which drivers are reserved. In this manner, they cannot be used by applications via file opens. The timer used by the hardlockup detector should be marked as reserved. Also, hpet_msi_capability_lookup() populates another data structure which is used when obtaining an unused timer for a HPET clock event. The timer used by the hardlockup detector should not be included in such data structure. Is this the explanation you would like to see? If yes, I will include it in the changelog. Thanks and BR, Ricardo