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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 B957BC433DF for ; Mon, 15 Jun 2020 18:32:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FC712071A for ; Mon, 15 Jun 2020 18:32:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="kZsZQvXl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731336AbgFOScZ (ORCPT ); Mon, 15 Jun 2020 14:32:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47368 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729354AbgFOScZ (ORCPT ); Mon, 15 Jun 2020 14:32:25 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0AAF6C061A0E for ; Mon, 15 Jun 2020 11:32:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kaLeQNKpwo/3pmt93qdeNrph7VCKxinWeBQB+muxlqU=; b=kZsZQvXl1NJZtySSQyofXqG2gJ LGW3VjHm9TuX25UqvO3KZKb2oOIY9GxryxwgyWiyhctAhFfedcv/u0AMokGAfuDcuQv/YwEGvsQmY 8hielzOiarmpwSn/5Z/0ZHjthHpnyNcIvvdozZPWoKwXF1+6ZCXlGxvI5cc6bKSJLMgkeQfJy9onI UNvacJvt2GszmscxRPRxdOJ3tSlgyXdm46wtChlF5IIN4RMh0tlBKzaD0+BDmhBAEVFIMAXXXwcY2 cISoF7L3RZDb4UNipJqrTeB82lsBma2Gf1fHVAikvl9tjy6NvvycYEJ6lHhJjlERcYaO3c4E8tvMX H2PwgC9A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jkttx-000598-1L; Mon, 15 Jun 2020 18:32:09 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C7A7430604B; Mon, 15 Jun 2020 20:32:04 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B5E05203DCA15; Mon, 15 Jun 2020 20:32:04 +0200 (CEST) Date: Mon, 15 Jun 2020 20:32:04 +0200 From: Peter Zijlstra To: "Raj, Ashok" 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 Subject: Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID Message-ID: <20200615183204.GE2531@hirez.programming.kicks-ass.net> 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> <20200615181921.GA33928@otc-nc-03> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200615181921.GA33928@otc-nc-03> 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 11:19:21AM -0700, Raj, Ashok wrote: > 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. Why do you need a TIF flag? Why not any other random flag in current?