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 A469AC433DB for ; Wed, 3 Feb 2021 10:29:05 +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 F409F64E38 for ; Wed, 3 Feb 2021 10:29:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F409F64E38 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:36528 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7FPD-0000H7-VI for qemu-devel@archiver.kernel.org; Wed, 03 Feb 2021 05:29:03 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:40394) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7FOL-00083i-JB for qemu-devel@nongnu.org; Wed, 03 Feb 2021 05:28:09 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:31110) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7FOK-0008CG-0v for qemu-devel@nongnu.org; Wed, 03 Feb 2021 05:28:09 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612348087; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=p2+qz0DjWkEkbZPan4bMlbGQBE07zRWTPTtmhEpp3FE=; b=FfbdOH93doT9duM3RopfLNVo2dkXkd8nN6tF/0QB1HWkJFadKRGZ1/0VSFf60BXNf9xGFA CaYN4pK82sPc2MQbndJkU1ZSkijvf93muggwjO5myeTZSiA8C9oQGwZ/r6XG10iNZFKC/2 siStd7is3AZtzUAyT6eU9/xcze+IQ9c= 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-402-ddn9cbMbOAaMmGS_7tbM5w-1; Wed, 03 Feb 2021 05:28:03 -0500 X-MC-Unique: ddn9cbMbOAaMmGS_7tbM5w-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 589DC107ACE4; Wed, 3 Feb 2021 10:28:02 +0000 (UTC) Received: from work-vm (ovpn-115-70.ams2.redhat.com [10.36.115.70]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CDA0D62461; Wed, 3 Feb 2021 10:28:00 +0000 (UTC) Date: Wed, 3 Feb 2021 10:27:58 +0000 From: "Dr. David Alan Gilbert" To: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: ARM Snapshots Not Backwards-Compatible Message-ID: <20210203102758.GC2950@work-vm> References: <153e5c54-f8bf-d088-502d-502309f5d2a6@redhat.com> MIME-Version: 1.0 In-Reply-To: <153e5c54-f8bf-d088-502d-502309f5d2a6@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=dgilbert@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=-0.386, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: , Cc: Peter Maydell , Andrew Jones , Juan Quintela , qemu-devel@nongnu.org, Aaron Lindsay , qemu-arm Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Philippe Mathieu-Daudé (philmd@redhat.com) wrote: > Cc'ing migration team and qemu-arm@ list. I'll have to leave the detail of that to the ARM peole; but from a migration point of view I think we do want the 64 bit ARM migrations to be stable now. Please tie incompatible changes to machine types. Dave > On 2/3/21 5:01 AM, Aaron Lindsay wrote: > > Hello, > > > > I'm attempting to restore an AArch64 snapshot taken on QEMU 4.1.0 on > > QEMU 5.2.0, using system mode. My previous impression, possibly from > > https://wiki.qemu.org/Features/Migration/Troubleshooting#Basics was that > > this ought to work: > > > >> Note that QEMU supports migrating forward between QEMU versions > > > > Note that I'm using qemu-system-aarch64 with -loadvm. > > > > However, I've run into several issues I thought I should report. The > > first of them was that this commit changed the address of CBAR, which > > resulted in a mismatch of the register IDs in `cpu_post_load` in > > target/arm/machine.c: > > https://patchwork.kernel.org/project/qemu-devel/patch/20190927144249.29999-2-peter.maydell@linaro.org/ > > > > The second was that several system registers have changed which bits are > > allowed to be written in different circumstances, seemingly as a result > > of a combination of bugfixes and implementation of additional behavior. > > These hit errors detected in `write_list_to_cpustate` in > > target/arm/helper.c. > > > > The third is that meanings of the bits in env->features (as defined by > > `enum arm_features` in target/arm/cpu.h) has shifted. For example, > > ARM_FEATURE_PXN, ARM_FEATURE_CRC, ARM_FEATURE_VFP, ARM_FEATURE_VFP3, > > ARM_FEATURE_VFP4 have all been removed and ARM_FEATURE_V8_1M has been > > added since 4.1.0. Heck, even I have added a field there in the past. > > Unfortunately, these additions/removals mean that when env->features is > > saved on one version and restored on another the bits can mean different > > things. Notably, the removal of the *VFP features means that a snapshot > > of a CPU reporting it supports ARM_FEATURE_VFP3 on 4.1.0 thinks it's now > > ARM_FEATURE_M on 5.2.0! > > > > My guess, given the numerous issues and the additional complexity > > required to properly implement backwards-compatible snapshotting, is > > that this is not a primary goal. However, if it is a goal, what steps > > can/should we take to support it more thoroughly? > > > > Thanks! > > > > -Aaron > > > > p.s. Now for an admission: the snapshots I'm testing with were > > originally taken with `-cpu max`. This was unintentional, and I > > understand if the response is that I can't expect `-cpu max` checkpoints > > to work across QEMU versions... but I also don't think that all of these > > issues can be blamed on that (notably CBAR and env->features). > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK