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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 798AEC4332E for ; Thu, 19 Mar 2020 19:27:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 505A42071C for ; Thu, 19 Mar 2020 19:27:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727432AbgCST07 (ORCPT ); Thu, 19 Mar 2020 15:26:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:47832 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726785AbgCST07 (ORCPT ); Thu, 19 Mar 2020 15:26:59 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id B4686AD03; Thu, 19 Mar 2020 19:26:56 +0000 (UTC) Date: Thu, 19 Mar 2020 20:26:54 +0100 From: Joerg Roedel To: Andy Lutomirski Cc: Joerg Roedel , X86 ML , "H. Peter Anvin" , Dave Hansen , Peter Zijlstra , Thomas Hellstrom , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , LKML , kvm list , Linux Virtualization Subject: Re: [PATCH 70/70] x86/sev-es: Add NMI state tracking Message-ID: <20200319192654.GD611@suse.de> References: <20200319091407.1481-1-joro@8bytes.org> <20200319091407.1481-71-joro@8bytes.org> <20200319160749.GC5122@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 19, 2020 at 11:40:39AM -0700, Andy Lutomirski wrote: > Nope. A nested NMI will reset the interrupted NMI's return frame to > cause it to run again when it's done. I don't think this will have > any real interaction with #VC. There's no longjmp() here. Ahh, so I misunderstood that part, in this case your proposal of sending the NMI-complete message right at the beginning of do_nmi() should work just fine. I will test this and see how it works out. > I certainly *like* preventing nesting, but I don't think we really > want a whole alternate NMI path just for a couple of messed-up AMD > generations. And the TF trick is not so pretty either. Indeed, if it could be avoided, it should. > > > > This causes us to pop the NMI frame off the stack. Assuming the NMI > > > restart logic is invoked (which is maybe impossible?), we get #DB, > > > which presumably is actually delivered. And we end up on the #DB > > > stack, which might already have been in use, so we have a potential > > > increase in nesting. Also, #DB may be called from an unexpected > > > context. > > > > An SEV-ES hypervisor is required to intercept #DB, which means that the > > #DB exception actually ends up being a #VC exception. So it will not end > > up on the #DB stack. > > With your patch set, #DB doesn't seem to end up on the #DB stack either. Right, it does not use the #DB stack or shift-ist stuff. Maybe it should, is this needed for anything else than making entry code debugable by kgdb? Regards, Joerg