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=-0.8 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 6E0A9C433DF for ; Tue, 23 Jun 2020 11:50:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 474102078E for ; Tue, 23 Jun 2020 11:50:52 +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="EDvXpjRw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732585AbgFWLuu (ORCPT ); Tue, 23 Jun 2020 07:50:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732225AbgFWLuu (ORCPT ); Tue, 23 Jun 2020 07:50:50 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B441CC061573; Tue, 23 Jun 2020 04:50:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=aiVkeicD79xrHH2MDVHjdOtjMnN8FcgFYepOS8k0muE=; b=EDvXpjRwRiWz5VfLeVl7JzHg3f x4dHtqMUkLsONa0nUGU8wT3Ft9ryJmQ5THUfSCggkT3OzDNJlDqGXdOUBd+TRGH85/sOLi5lDHl9G lOV1OE1pxKcRl3T92sVXNqPNFTB7t3KsMUo98+uLsk+SlcUpsCQxejCEMg40knl3T2IkFX2bzXPeZ xnJ5wgAWm9Z7m2KkkmdtZJVdJOhzLBBBlYoCOoR3z4BH8prfDBy/FdcOzSpostBvsjevokivifqnF V32Tzv5H/+7uSj+u0LdpX8PXd9vugeJH8ciDz2WAGJbRGbYz2FDxDn1Ddqrf8P0/ml1+v+KoOoQKM QKuRBYlA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jnhRQ-0002Cb-IP; Tue, 23 Jun 2020 11:50:16 +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 A0F95300F28; Tue, 23 Jun 2020 13:50:14 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 860502370F7D2; Tue, 23 Jun 2020 13:50:14 +0200 (CEST) Date: Tue, 23 Jun 2020 13:50:14 +0200 From: Peter Zijlstra To: Joerg Roedel Cc: Andy Lutomirski , Joerg Roedel , Dave Hansen , Tom Lendacky , Mike Stunes , Dan Williams , Dave Hansen , "H. Peter Anvin" , Juergen Gross , Jiri Slaby , Kees Cook , kvm list , LKML , Thomas Hellstrom , Linux Virtualization , X86 ML , Sean Christopherson , Andrew Cooper Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace) Message-ID: <20200623115014.GE4817@hirez.programming.kicks-ass.net> References: <20200425191032.GK21900@8bytes.org> <910AE5B4-4522-4133-99F7-64850181FBF9@amacapital.net> <20200425202316.GL21900@8bytes.org> <20200623094519.GF31822@suse.de> <20200623104559.GA4817@hirez.programming.kicks-ass.net> <20200623111107.GG31822@suse.de> <20200623111443.GC4817@hirez.programming.kicks-ass.net> <20200623114324.GA14101@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623114324.GA14101@suse.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 23, 2020 at 01:43:24PM +0200, Joerg Roedel wrote: > On Tue, Jun 23, 2020 at 01:14:43PM +0200, Peter Zijlstra wrote: > > On Tue, Jun 23, 2020 at 01:11:07PM +0200, Joerg Roedel wrote: > > > > The v3 patchset implements an unconditional shift of the #VC IST entry > > > in the NMI handler, before it can trigger a #VC exception. > > > > Going by that other thread -- where you said that any memory access can > > trigger a #VC, there just isn't such a guarantee. > > As I wrote in the other mail, this can only happen when SNP gets enabled > (which is follow-on work to this) and is handled by a stack recursion > check in the #VC handler. > > The reason I mentioned the #VC-anywhere case is to make it more clear > why #VC needs an IST handler. If SNP is the sole reason #VC needs to be IST, then I'd strongly urge you to only make it IST if/when you try and make SNP happen, not before. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace) Date: Tue, 23 Jun 2020 13:50:14 +0200 Message-ID: <20200623115014.GE4817@hirez.programming.kicks-ass.net> References: <20200425191032.GK21900@8bytes.org> <910AE5B4-4522-4133-99F7-64850181FBF9@amacapital.net> <20200425202316.GL21900@8bytes.org> <20200623094519.GF31822@suse.de> <20200623104559.GA4817@hirez.programming.kicks-ass.net> <20200623111107.GG31822@suse.de> <20200623111443.GC4817@hirez.programming.kicks-ass.net> <20200623114324.GA14101@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20200623114324.GA14101@suse.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" To: Joerg Roedel Cc: Juergen Gross , Tom Lendacky , Thomas Hellstrom , X86 ML , Mike Stunes , Kees Cook , kvm list , Andrew Cooper , Joerg Roedel , Dave Hansen , LKML , Sean Christopherson , Linux Virtualization , Dave Hansen , Andy Lutomirski , "H. Peter Anvin" , Dan Williams , Jiri Slaby List-Id: virtualization@lists.linuxfoundation.org On Tue, Jun 23, 2020 at 01:43:24PM +0200, Joerg Roedel wrote: > On Tue, Jun 23, 2020 at 01:14:43PM +0200, Peter Zijlstra wrote: > > On Tue, Jun 23, 2020 at 01:11:07PM +0200, Joerg Roedel wrote: > > > > The v3 patchset implements an unconditional shift of the #VC IST entry > > > in the NMI handler, before it can trigger a #VC exception. > > > > Going by that other thread -- where you said that any memory access can > > trigger a #VC, there just isn't such a guarantee. > > As I wrote in the other mail, this can only happen when SNP gets enabled > (which is follow-on work to this) and is handled by a stack recursion > check in the #VC handler. > > The reason I mentioned the #VC-anywhere case is to make it more clear > why #VC needs an IST handler. If SNP is the sole reason #VC needs to be IST, then I'd strongly urge you to only make it IST if/when you try and make SNP happen, not before.