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=-5.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 39279C4332F for ; Fri, 3 Sep 2021 15:33:36 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D29A86108E for ; Fri, 3 Sep 2021 15:33:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D29A86108E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:56230 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mMBCB-00075O-26 for qemu-devel@archiver.kernel.org; Fri, 03 Sep 2021 11:33:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51016) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mMB9r-0004AP-Mi for qemu-devel@nongnu.org; Fri, 03 Sep 2021 11:31:11 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:38837) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mMB9p-0004PL-R5 for qemu-devel@nongnu.org; Fri, 03 Sep 2021 11:31:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1630683068; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=CzPb8MlbLx41oQqysfJ8QyV0MvR1gCZguZRQ8mTaaK4=; b=cerqXlKcOvHEbWr9RPnfwYboKkLk/4G/V0Q4BehAHj9ChgaCTrotff+dXUZzwtFAFnkuC+ RSUTrVvJyd0/VeLzpUS9r6M26FeE1CTmH0ZsCRwTNBNsOkNhWjhHiosobGoDeW1lZ27Zpo PXj9E9hxtjio1eNTJa9s+jXK6pCdgFI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-588-uJrZ-_7SOISk6KCCwMLCZQ-1; Fri, 03 Sep 2021 11:31:02 -0400 X-MC-Unique: uJrZ-_7SOISk6KCCwMLCZQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2DC9384A5E1; Fri, 3 Sep 2021 15:31:01 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.241]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A27195D9D3; Fri, 3 Sep 2021 15:30:50 +0000 (UTC) Date: Fri, 3 Sep 2021 16:30:48 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Michael Roth Subject: Re: [RFC PATCH v2 12/12] i386/sev: update query-sev QAPI format to handle SEV-SNP Message-ID: References: <20210826222627.3556-1-michael.roth@amd.com> <20210826222627.3556-13-michael.roth@amd.com> <87tuj4qt71.fsf@dusky.pond.sub.org> <20210903151316.zveiegbo42o2gttq@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210903151316.zveiegbo42o2gttq@amd.com> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.392, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Tom Lendacky , Brijesh Singh , Eduardo Habkost , kvm@vger.kernel.org, "Michael S . Tsirkin" , Connor Kuehl , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , James Bottomley , Markus Armbruster , qemu-devel@nongnu.org, Dov Murik , Paolo Bonzini , Eric Blake , "Dr . David Alan Gilbert" , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Sep 03, 2021 at 10:13:16AM -0500, Michael Roth wrote: > On Wed, Sep 01, 2021 at 04:14:10PM +0200, Markus Armbruster wrote: > > Michael Roth writes: > > > > > Most of the current 'query-sev' command is relevant to both legacy > > > SEV/SEV-ES guests and SEV-SNP guests, with 2 exceptions: > > > > > > - 'policy' is a 64-bit field for SEV-SNP, not 32-bit, and > > > the meaning of the bit positions has changed > > > - 'handle' is not relevant to SEV-SNP > > > > > > To address this, this patch adds a new 'sev-type' field that can be > > > used as a discriminator to select between SEV and SEV-SNP-specific > > > fields/formats without breaking compatibility for existing management > > > tools (so long as management tools that add support for launching > > > SEV-SNP guest update their handling of query-sev appropriately). > > > > Technically a compatibility break: query-sev can now return an object > > that whose member @policy has different meaning, and also lacks @handle. > > > > Matrix: > > > > Old mgmt app New mgmt app > > Old QEMU, SEV/SEV-ES good good(1) > > New QEMU, SEV/SEV-ES good(2) good > > New QEMU, SEV-SNP bad(3) good > > > > Notes: > > > > (1) As long as the management application can cope with absent member > > @sev-type. > > > > (2) As long as the management application ignores unknown member > > @sev-type. > > > > (3) Management application may choke on missing member @handle, or > > worse, misinterpret member @policy. Can only happen when something > > other than the management application created the SEV-SNP guest (or the > > user somehow made the management application create one even though it > > doesn't know how, say with CLI option passthrough, but that's always > > fragile, and I wouldn't worry about it here). > > > > I think (1) and (2) are reasonable. (3) is an issue for management > > applications that support attaching to existing guests. Thoughts? > > Hmm... yah I hadn't considering 'old mgmt' trying to interact with a SNP > guest started through some other means. > > Don't really see an alternative other than introducing a new > 'query-sev-snp', but that would still leave 'old mgmt' broken, since > it might still call do weird stuff like try to interpret the SNP policy > as an SEV/SEV-ES and end up with some very unexpected results. So if I > did go this route, I would need to have QMP begin returning an error if > query-sev is run against an SNP guest. But currently for non-SEV guests > it already does: > > error_setg(errp, "SEV feature is not available") > > so 'old mgmt' should be able to handle the error just fine. > > Would that approach be reasonable? This ties into the question I've just sent in my other mail. If the hardware strictly requires that guest are created in SEV-SNP mode only, and will not support SEV/SEV-ES mode, then we need to ensure "query-sev" reports the feature as not-available, so that existing mgmt apps don't try to use SEV/SEV-ES. If the SEV-SNP hardware is functionally back-compatible with a gues configured in SEV/SEV-ES mode, then we souldn't need a new command, just augment th eexisting command with additional field(s), to indicate existance of SEV-SNP features. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|