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 1B091C433E1 for ; Tue, 23 Jun 2020 13:59:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EDA7520720 for ; Tue, 23 Jun 2020 13:59:57 +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="QQqHr4Is" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732730AbgFWN7x (ORCPT ); Tue, 23 Jun 2020 09:59:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49958 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732687AbgFWN7x (ORCPT ); Tue, 23 Jun 2020 09:59:53 -0400 Received: from casper.infradead.org (unknown [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 68041C061573; Tue, 23 Jun 2020 06:59:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=vWFZnmE8muSdoNv/rlN/zg+D4ErnvxS0/K6mx8ubUo4=; b=QQqHr4IslmzJW09bxhv1Ibqy14 exvYtd4xNdVggaYQ7J+3Ux3ltaf/4zgfPk5nlZA57lRVghngQDw3jFFH1qd4JvYdxS7Gzuffi/EXa pJCr6X0+J6sOE4R312V3eYLvvquor1WCpbl3LiqTvvZdXDG5QgUdiRucg2Mg1GfrE0aqshfm7iISX 4vueqvSBN9VUfaOsOehNU2M6fjlHD+xQrwa7GWTRoizDBchrv0ovCNNMo+E0mT0CThS8FbkY+19V5 PlUbml1JCC4gS4MGCLinM5pdDFLQRUkizCTYkXF/HLVQpJDKZXWrZLBOsC944fXDC+vkIXa/9RrRU GcD0Wmtw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jnjSI-0004Rt-F5; Tue, 23 Jun 2020 13:59:18 +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 73420300F28; Tue, 23 Jun 2020 15:59:16 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6467323CBF701; Tue, 23 Jun 2020 15:59:16 +0200 (CEST) Date: Tue, 23 Jun 2020 15:59:16 +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: <20200623135916.GI4817@hirez.programming.kicks-ass.net> References: <20200425202316.GL21900@8bytes.org> <20200428075512.GP30814@suse.de> <20200623110706.GB4817@hirez.programming.kicks-ass.net> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623134003.GD14101@suse.de> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Jun 23, 2020 at 03:40:03PM +0200, Joerg Roedel wrote: > On Tue, Jun 23, 2020 at 02:52:01PM +0200, Peter Zijlstra wrote: > > You only have that guarantee when any SNP #VC from kernel is an > > automatic panic. But in that case, what's the point of having the > > recursion count? > > It is not a recursion count, it is a stack-recursion check. Basically > walk down the stack and look if your current stack is already in use. > Yes, this can be optimized, but that is what is needed. > > IIRC the current prototype code for SNP just pre-validates all memory in > the VM and doesn't support moving pages around on the host. So any #VC > SNP exception would be fatal, yes. > > In a scenario with on-demand validation of guest pages and support for > guest-assisted page-moving on the HV side it would be more complicated. > Basically all memory that is accessed during #VC exception handling must > stay validated at all times, including the IST stack. > > So saying this, I don't understand why _all_ SNP #VC exceptions from > kernel space must be fatal? Ah, because I hadn't thought of the stack-recursion check. So basically when your exception frame points to your own IST, you die. That sounds like something we should have in generic IST code.