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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id E2351C38150 for ; Wed, 10 Jul 2024 07:17:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sRRZD-0003cq-3l; Wed, 10 Jul 2024 03:16:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sRRZ5-0003BW-2e for qemu-devel@nongnu.org; Wed, 10 Jul 2024 03:16:36 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sRRZ0-0000pv-0N for qemu-devel@nongnu.org; Wed, 10 Jul 2024 03:16:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1720595787; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=I5ay2VRUwip0nMjiuiTGOO05fCeJ7Uz6LJBILh9iWug=; b=RHJQ0OWinHmwkyntPU2Ef9K0DR5KBtLvl2kzaDnMPIkHxaHAGYsYcAsDnbwZakBkyRH/Be c5KmgLFWMOB8bfZmgXihBApT3elWn0P31OwLT3+1xtvQqjArUbu/K7ImZdbNbiNezRY/2b BRLcvbAU9OVRkpkx61o5fr/86FZgmxQ= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-682-aQim4U5ANZ6EETATUXyr6A-1; Wed, 10 Jul 2024 03:16:21 -0400 X-MC-Unique: aQim4U5ANZ6EETATUXyr6A-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C75AB1954207; Wed, 10 Jul 2024 07:16:20 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.46]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 335F219560AE; Wed, 10 Jul 2024 07:16:17 +0000 (UTC) Date: Wed, 10 Jul 2024 08:16:14 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Michael Roth Cc: Paolo Bonzini , qemu-devel@nongnu.org, kvm@vger.kernel.org Subject: Re: [PATCH] i386/sev: Don't allow automatic fallback to legacy KVM_SEV*_INIT Message-ID: References: <20240704000019.3928862-1-michael.roth@amd.com> <20240710040319.6bvsy4x7mnnuxled@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240710040319.6bvsy4x7mnnuxled@amd.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.144, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Jul 09, 2024 at 11:03:19PM -0500, Michael Roth wrote: > On Thu, Jul 04, 2024 at 11:53:33AM +0200, Paolo Bonzini wrote: > > On Thu, Jul 4, 2024 at 11:39 AM Daniel P. Berrangé wrote: > > > > The debug_swap parameter simply could not be enabled in the old API > > > > without breaking measurements. The new API *is the fix* to allow using > > > > it (though QEMU doesn't have the option plumbed in yet). There is no > > > > extensibility. > > > > > > > > Enabling debug_swap by default is also a thorny problem; it cannot be > > > > enabled by default because not all CPUs support it, and also we'd have > > > > the same problem that we cannot enable debug_swap on new machine types > > > > without requiring a new kernel. Tying the default to the -cpu model > > > > would work but it is confusing. > > > > > > Presumably we can tie it to '-cpu host' without much problem, and > > > then just leave it as an opt-in feature flag for named CPU models. > > > > '-cpu host' for SEV-SNP is also problematic, since CPUID is part of > > the measurement. It's okay for starting guests in a quick and dirty > > manner, but it cannot be used if measurement is in use. > > > > It's weird to have "-cpu" provide the default for "-object", since > > -object is created much earlier than CPUs. But then "-cpu" itself is > > weird because it's a kind of "factory" for future objects. Maybe we > > should redo the same exercise I did to streamline machine > > initialization, this time focusing on -cpu/-machine/-accel, to > > understand the various phases and where sev-{,snp-}guest > > initialization fits. > > > > > > I think it's reasonable if the fix is displayed right into the error > > > > message. It's only needed for SEV-ES though, SEV can use the old and > > > > new APIs interchangeably. > > > > > > FYI currently it is proposed to unconditionally force set legacy-vm-type=true > > > in libvirt, so QEMU guests would *never* use the new ioctl, to fix what we > > > consider to be a QEMU / kernel guest ABI regression. > > > > Ok, so it's probably best to apply both this and your patch for now. > > Later debug-swap can be enabled and will automatically disable > > legacy-vm-type if the user left it to the default. > > I think this seems like the ideal default behavior, where QEMU will > continue to stick with legacy interface unless the user specifically > enables a new option like debug-swap that relies on KVM_SEV_INIT2. > So I reworked this patch to make legacy-vm-type an OnOffAuto field, > where 'auto' implements the above semantics, and 'on'/'off' continue > to behave as they do here in v1. > > At the moment, since QEMU doesn't actually expose anything that requires > KVM_SEV_INIT2 for SEV-ES, setting legacy-vm-type to 'auto' or 'on' end > up being equivalent, but by defaulting to 'auto' things will continue to > "just work" on the libvirt side even when new features are enabled. And > by adding a bit of that infrastructure now it's less likely that some > option gets exposed in a way that doesn't abide by the above semantics. > > So as part of v2 I switched the default for 9.1+ to 'auto'. But if > v1+Daniel's patch is still preferred that should be fine too. I think your v2 patch is good on its own. It avoids the issues that concerned me and has sensible future behaviour too. With 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 :|