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 860D4C433DF for ; Tue, 23 Jun 2020 15:52:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6064F2076E for ; Tue, 23 Jun 2020 15:52:39 +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="P+jdsz0u" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733036AbgFWPwg (ORCPT ); Tue, 23 Jun 2020 11:52:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732942AbgFWPwf (ORCPT ); Tue, 23 Jun 2020 11:52:35 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4804BC061573; Tue, 23 Jun 2020 08:52:35 -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=V+I5M6T0vX0U3AsFDgchL+f1L6gn7BSv3aERPVrjnPY=; b=P+jdsz0ucfshSY+SPQ8CRHAJD+ x4g4UkTqpdDwyLW7IHndErlpvnUEKSuBos0fi391zScfBZg4cN3Tj56VCg4zTawV5zzyskojPa2Ns 70wOMACbqtQ9ryX6O0y7oKh9zeN9KjCY0Ub914IGNKVUaC+FMR7ZXF+PAlT+Fwbre1YSz+Bb5Cw1e kOddoPFwBkU7dqyg0y8k0Oo4m/QPWh+rK3TG9b+jLQt4W6zcbukO7JWa0QB/SH1iYn/GP3FlmQmt6 Wq3nNq/PmV/3mUlKi5YRLVU3pI5DK8KiKa0eVG8IPKGe3gsc21N+y/wnvkRZnTqpp9StJibYoU2Sd 8cWEhqJg==; 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 1jnlDS-0001Ra-Ti; Tue, 23 Jun 2020 15:52:07 +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 F0C27306E5C; Tue, 23 Jun 2020 17:52:04 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DF0EA234EBA5D; Tue, 23 Jun 2020 17:52:04 +0200 (CEST) Date: Tue, 23 Jun 2020 17:52:04 +0200 From: Peter Zijlstra To: Andrew Cooper Cc: Joerg Roedel , 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 Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace) Message-ID: <20200623155204.GO4817@hirez.programming.kicks-ass.net> References: <20200623113007.GH31822@suse.de> <20200623114818.GD4817@hirez.programming.kicks-ass.net> <20200623120433.GB14101@suse.de> <20200623125201.GG4817@hirez.programming.kicks-ass.net> <20200623134003.GD14101@suse.de> <20200623135916.GI4817@hirez.programming.kicks-ass.net> <20200623145344.GA117543@hirez.programming.kicks-ass.net> <20200623145914.GF14101@suse.de> <20200623152326.GL4817@hirez.programming.kicks-ass.net> <56af2f70-a1c6-aa64-006e-23f2f3880887@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56af2f70-a1c6-aa64-006e-23f2f3880887@citrix.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Jun 23, 2020 at 04:39:26PM +0100, Andrew Cooper wrote: > On 23/06/2020 16:23, Peter Zijlstra wrote: > > On Tue, Jun 23, 2020 at 04:59:14PM +0200, Joerg Roedel wrote: > >> Yes, this is a start, it doesn't cover the case where the NMI stack is > >> in-between, so I think you need to walk down regs->sp too. > > That shouldn't be possible with the current code, I think. > > NMI; #MC; Anything which IRET but isn't fatal - #DB, or #BP from > patching, #GP from *_safe(), etc; NMI > > Sure its a corner case, but did you hear that IST is evil? Isn't current #MC unconditionally fatal from kernel? But yes, I was sorta aware people want that changed. And yes, NMI can recurse, mostly on #BP and #PF. Like I wrote, its broken vs #MC. But Joerg was talking about IST recursion with NMI in the middle, something like: #DB, NMI, #DB, and not already being fatal. This one in particular is ruled out by #DB itself clearing DR7 (but NMI would also do that). > P.S. did you also hear that with Rowhammer, userspace has a nonzero > quantity of control over generating #MC, depending on how ECC is > configured on the platform. Yes, excellent stuff.