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,URIBL_BLOCKED,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 959D5C433DF for ; Mon, 15 Jun 2020 18:55:35 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (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 4147F20656 for ; Mon, 15 Jun 2020 18:55:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4147F20656 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 0444688111; Mon, 15 Jun 2020 18:55:35 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id FRJkMkndusu1; Mon, 15 Jun 2020 18:55:33 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by whitealder.osuosl.org (Postfix) with ESMTP id 6C38587EBD; Mon, 15 Jun 2020 18:55:33 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 408E0C0888; Mon, 15 Jun 2020 18:55:33 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 89AD4C016E for ; Mon, 15 Jun 2020 18:55:31 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 583F425075 for ; Mon, 15 Jun 2020 18:55:31 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ndazAKCc2Wb3 for ; Mon, 15 Jun 2020 18:55:29 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by silver.osuosl.org (Postfix) with ESMTPS id D323824FFE for ; Mon, 15 Jun 2020 18:55:29 +0000 (UTC) IronPort-SDR: LgsKRjdNAPwqGTLTWjR7nxwHC1SiXhwgU54lqV7OktWmR7zfiO5FqcsOL+OLeTR6/fuJpqoEly 6TTCUj0/jSpg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2020 11:55:29 -0700 IronPort-SDR: 7AOfFl+Q9Zk9+pLDv+ctsLfdexol4Ooa9fms1lqtuvgDaDmflZdjgu5bI2sLLO96QFzKhPty0n Vry9GVkoZi+A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,515,1583222400"; d="scan'208";a="382630204" Received: from romley-ivt3.sc.intel.com ([172.25.110.60]) by fmsmga001.fm.intel.com with ESMTP; 15 Jun 2020 11:55:30 -0700 Date: Mon, 15 Jun 2020 11:55:29 -0700 From: Fenghua Yu To: Peter Zijlstra Subject: Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID Message-ID: <20200615185529.GD13792@romley-ivt3.sc.intel.com> 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> <20200615181259.GC13792@romley-ivt3.sc.intel.com> <20200615183116.GD2531@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200615183116.GD2531@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Cc: Dave Hansen , H Peter Anvin , Dave Jiang , Ashok Raj , x86 , amd-gfx , Ingo Molnar , Ravi V Shankar , Yu-cheng Yu , Andrew Donnellan , Borislav Petkov , Thomas Gleixner , Tony Luck , linuxppc-dev , Felix Kuehling , linux-kernel , iommu@lists.linux-foundation.org, Jacob Jun Pan , Frederic Barrat , David Woodhouse X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Hi, Peter, On Mon, Jun 15, 2020 at 08:31:16PM +0200, Peter Zijlstra wrote: > On Mon, Jun 15, 2020 at 11:12:59AM -0700, Fenghua Yu 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? > > > > My concern is TIF flags are precious (only 3 slots available). Defining > > a new TIF flag may be not worth it while rdmsr() can check if PASID > > is valid in the MSR. And performance here might not be a big issue > > in #GP. > > > > But if you think using TIF flag is better, I can define a new TIF flag > > and maintain it per thread (init 0 when clone()/fork(), set 1 in fixup()). > > Then we can avoid using rdmsr() to check valid PASID in the MSR. > > WHY ?!?! What do you need a TIF flag for? We need "a way" to check if the per thread MSR has a valid PASID. If yes, no need to fix up the MSR (wrmsr()), and let other handler to handle the #GP. Otherwise, apply the heuristics and fix up the MSR and exit the #GP. The way to check the valid PASID in the MSR is rdmsr() in this series. A TIF flag will be much faster than rdmsr() and seems a sutiable way to check valid PASID status per thread. That's why it could replace rdmsr() to check PASID in the MSR. Or do you suggest to add a random new flag in struct thread_info instead of a TIF flag? Thanks. -Fenghua _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu