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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D462EC433F5 for ; Wed, 2 Feb 2022 11:38:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241292AbiBBLi1 (ORCPT ); Wed, 2 Feb 2022 06:38:27 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:31338 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231815AbiBBLiZ (ORCPT ); Wed, 2 Feb 2022 06:38:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643801904; h=from:from: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=apYEsUqnAhxfwffcP4EQfPNRfUo+jrOWRHDs7r/K2Gk=; b=KLQz0BJkt59gt54kV2VQWbsZVP8BXMiwaJ4ApRC6F0mIOaVmfeTGAaLZHIaMQjQ/g5spTx mwOV58/kBIJVZZdsbtXaK9qmjF+XiqGRgcxbPELUJZCUo6OfcPUPLlx+UdZjzb/3Wm9kEq rEGcLIgeHQn93vEEePSGeED4uu4jMvE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-67-CnyO_hl-OOmkDHqEUQQqRQ-1; Wed, 02 Feb 2022 06:38:19 -0500 X-MC-Unique: CnyO_hl-OOmkDHqEUQQqRQ-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 9FC78802925; Wed, 2 Feb 2022 11:38:17 +0000 (UTC) Received: from localhost (unknown [10.39.194.123]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 41D8178A95; Wed, 2 Feb 2022 11:38:09 +0000 (UTC) From: Cornelia Huck To: Alex Williamson Cc: Jason Gunthorpe , Yishai Hadas , bhelgaas@google.com, saeedm@nvidia.com, linux-pci@vger.kernel.org, kvm@vger.kernel.org, netdev@vger.kernel.org, kuba@kernel.org, leonro@nvidia.com, kwankhede@nvidia.com, mgurtovoy@nvidia.com, maorg@nvidia.com Subject: Re: [PATCH V6 mlx5-next 10/15] vfio: Remove migration protocol v1 In-Reply-To: <20220201160106.0760bfea.alex.williamson@redhat.com> Organization: Red Hat GmbH References: <20220130160826.32449-1-yishaih@nvidia.com> <20220130160826.32449-11-yishaih@nvidia.com> <874k5izv8m.fsf@redhat.com> <20220201121325.GB1786498@nvidia.com> <87sft2yd50.fsf@redhat.com> <20220201160106.0760bfea.alex.williamson@redhat.com> User-Agent: Notmuch/0.34 (https://notmuchmail.org) Date: Wed, 02 Feb 2022 12:38:07 +0100 Message-ID: <875ypxxzvk.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Feb 01 2022, Alex Williamson wrote: > On Tue, 01 Feb 2022 13:39:23 +0100 > Cornelia Huck wrote: > >> On Tue, Feb 01 2022, Jason Gunthorpe wrote: >> >> > On Tue, Feb 01, 2022 at 12:23:05PM +0100, Cornelia Huck wrote: >> >> On Sun, Jan 30 2022, Yishai Hadas wrote: >> >> >> >> > From: Jason Gunthorpe >> >> > >> >> > v1 was never implemented and is replaced by v2. >> >> > >> >> > The old uAPI definitions are removed from the header file. As per Linus's >> >> > past remarks we do not have a hard requirement to retain compilation >> >> > compatibility in uapi headers and qemu is already following Linus's >> >> > preferred model of copying the kernel headers. >> >> >> >> If we are all in agreement that we will replace v1 with v2 (and I think >> >> we are), we probably should remove the x-enable-migration stuff in QEMU >> >> sooner rather than later, to avoid leaving a trap for the next >> >> unsuspecting person trying to update the headers. >> > >> > Once we have agreement on the kernel patch we plan to send a QEMU >> > patch making it support the v2 interface and the migration >> > non-experimental. We are also working to fixing the error paths, at >> > least least within the limitations of the current qemu design. >> >> I'd argue that just ripping out the old interface first would be easier, >> as it does not require us to synchronize with a headers sync (and does >> not require to synchronize a headers sync with ripping it out...) >> >> > The v1 support should remain in old releases as it is being used in >> > the field "experimentally". >> >> Of course; it would be hard to rip it out retroactively :) >> >> But it should really be gone in QEMU 7.0. >> >> Considering adding the v2 uapi, we might get unlucky: The Linux 5.18 >> merge window will likely be in mid-late March (and we cannot run a >> headers sync before the patches hit Linus' tree), while QEMU 7.0 will >> likely enter freeze in mid-late March as well. So there's a non-zero >> chance that the new uapi will need to be deferred to 7.1. > > > Agreed that v1 migration TYPE/SUBTYPE should live in infamy as > reserved, but I'm not sure why we need to make the rest of it a big > complicated problem. On one hand, leaving stubs for the necessary > structure and macros until QEMU gets updated doesn't seem so terrible. > Nor actually does letting the next QEMU header update cause build > breakages, which would probably frustrate the person submitting that > update, but it's not like QEMU hasn't done selective header updates in > the past. The former is probably the more friendly approach if we > don't outrage someone in the kernel community in the meantime. Leaving stubs in (while making it clear that v1 is not something you should use) seems like a good compromise. While we have done selective headers updates in QEMU in the past, I always found them painful, so I'd like to avoid that.