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_SANE_1 autolearn=no 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 AE31FC433DF for ; Mon, 15 Jun 2020 18:19:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88C98206DB for ; Mon, 15 Jun 2020 18:19:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731192AbgFOSTX (ORCPT ); Mon, 15 Jun 2020 14:19:23 -0400 Received: from mga06.intel.com ([134.134.136.31]:38592 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729124AbgFOSTW (ORCPT ); Mon, 15 Jun 2020 14:19:22 -0400 IronPort-SDR: aBEMWUl0iLwja3eT48E1NVfDaFVrH3V1FHc6yPFHzgptHAyqh6yGahzDm6tlu4T9sZ6Mgl5rHe jWh7HSzmunxw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2020 11:19:21 -0700 IronPort-SDR: SdtFHoff29V9KtkfxtvNK8UK0GFz3weIqBlZYoLU507VjZSQ/qwXtL4fCM6H4L+ZylJ6G3K3Og KpQCvO0hDJeg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,515,1583222400"; d="scan'208";a="382621179" Received: from otc-nc-03.jf.intel.com (HELO otc-nc-03) ([10.54.39.25]) by fmsmga001.fm.intel.com with ESMTP; 15 Jun 2020 11:19:21 -0700 Date: Mon, 15 Jun 2020 11:19:21 -0700 From: "Raj, Ashok" To: Peter Zijlstra Cc: Fenghua Yu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , David Woodhouse , Lu Baolu , Frederic Barrat , Andrew Donnellan , Felix Kuehling , Joerg Roedel , Dave Hansen , Tony Luck , Jacob Jun Pan , Dave Jiang , Yu-cheng Yu , Sohil Mehta , Ravi V Shankar , linux-kernel , x86 , iommu@lists.linux-foundation.org, amd-gfx , linuxppc-dev , Ashok Raj Subject: Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID Message-ID: <20200615181921.GA33928@otc-nc-03> References: <1592008893-9388-1-git-send-email-fenghua.yu@intel.com> <1592008893-9388-13-git-send-email-fenghua.yu@intel.com> <20200615075649.GK2497@hirez.programming.kicks-ass.net> <20200615154854.GB13792@romley-ivt3.sc.intel.com> <20200615160357.GA2531@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200615160357.GA2531@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 15, 2020 at 06:03:57PM +0200, Peter Zijlstra wrote: > > I don't get why you need a rdmsr here, or why not having one would > require a TIF flag. Is that because this MSR is XSAVE/XRSTOR managed? > > > > > + */ > > > > + rdmsrl(MSR_IA32_PASID, pasid_msr); > > > > + if (pasid_msr & MSR_IA32_PASID_VALID) > > > > + return false; > > > > + > > > > + /* Fix up the MSR if the MSR doesn't have a valid PASID. */ > > > > + wrmsrl(MSR_IA32_PASID, pasid | MSR_IA32_PASID_VALID); > > How much more expensive is the wrmsr over the rdmsr? Can't we just > unconditionally write the current PASID and call it a day? The reason to check the rdmsr() is because we are using a hueristic taking GP faults. If we already setup the MSR, but we get it a second time it means the reason is something other than PASID_MSR not being set. Ideally we should use the TIF_ to track this would be cheaper, but we were told those bits aren't easy to give out. Cheers, Ashok