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 3870CC433E0 for ; Mon, 15 Jun 2020 22:47:23 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DFB362074D for ; Mon, 15 Jun 2020 22:47:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DFB362074D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49m60S0N12zDqcS for ; Tue, 16 Jun 2020 08:47:20 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=intel.com (client-ip=134.134.136.31; helo=mga06.intel.com; envelope-from=ashok.raj@intel.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=intel.com Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 49m03V3WjVzDqLf for ; Tue, 16 Jun 2020 04:19:24 +1000 (AEST) IronPort-SDR: Hj6wevjBi4YFZ2Lx/bEme9AhX9myKWpcHYeWqIjEyQusmzS1ZlOI9HkpYWBwgNdI7cjc45pY+F XVxaUnlUaJgw== 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 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) X-Mailman-Approved-At: Tue, 16 Jun 2020 08:37:34 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Ravi V Shankar , Dave Hansen , H Peter Anvin , Dave Jiang , Ashok Raj , Joerg Roedel , x86 , amd-gfx , Ingo Molnar , Fenghua Yu , Yu-cheng Yu , Andrew Donnellan , Borislav Petkov , Sohil Mehta , Thomas Gleixner , Tony Luck , linuxppc-dev , Felix Kuehling , linux-kernel , iommu@lists.linux-foundation.org, Jacob Jun Pan , Frederic Barrat , David Woodhouse , Lu Baolu Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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