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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 17394C433DB for ; Wed, 3 Feb 2021 15:11:56 +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 3DDA064E4B for ; Wed, 3 Feb 2021 15:11:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3DDA064E4B 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]:38290 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7Jow-0000c9-4l for qemu-devel@archiver.kernel.org; Wed, 03 Feb 2021 10:11:54 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:35570) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7JoH-0008Qs-S6 for qemu-devel@nongnu.org; Wed, 03 Feb 2021 10:11:13 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:22467) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7JoE-0005OZ-Iw for qemu-devel@nongnu.org; Wed, 03 Feb 2021 10:11:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612365069; 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=UVqe9cxC/m6VcfnnUGqLOcKRO5UCgaV+uyZKsrd3sw8=; b=LGyIwgV1u4bCT67grJyk7rt/DLZXoZxNC0VMJIH1SneytdZt2QqzjYhXnd8DGVio9pQOEM qO4RObidR7u8sSYEaQMqEXGeq0QiDbAFaOiWWP5NssTcxGyya6AZt+nUFCXkoMee+A+fUl rsSMuUZjJLxh0KI+o5+sFIuryG8vyiA= 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-513-V-1ekkHsM3-HBNrf21gTFQ-1; Wed, 03 Feb 2021 10:11:05 -0500 X-MC-Unique: V-1ekkHsM3-HBNrf21gTFQ-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 94B5779ECB; Wed, 3 Feb 2021 15:11:02 +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 29D786267F; Wed, 3 Feb 2021 15:10:56 +0000 (UTC) Date: Wed, 3 Feb 2021 15:10:53 +0000 From: "Dr. David Alan Gilbert" To: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: ARM Snapshots Not Backwards-Compatible Message-ID: <20210203151053.GK2950@work-vm> References: <2572efa4-8aa3-32e4-7559-f93e6522d284@redhat.com> MIME-Version: 1.0 In-Reply-To: <2572efa4-8aa3-32e4-7559-f93e6522d284@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=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.539, 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_H3=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: 2.1.23 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: > On 2/3/21 3:58 PM, Aaron Lindsay wrote: > > On Feb 03 10:01, Peter Maydell wrote: > >>> 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! > >> > >> Ow. I didn't realize the env->features was in the migration state :-( > >> There is no reason for it to be, because it's a constant property > >> of the CPU. The easy fix is to replace > >> VMSTATE_UINT64(env.features, ARMCPU), > >> in target/arm/machine.c with whatever the syntax is for "ignore > >> 64 bits of data here". Then we'll ignore whatever is coming in > >> from the source, which we don't need, and we'll stop sending it > >> out if we're the destination. > > > > I'll look into this. > > I think this is: > > VMSTATE_UNUSED(sizeof(uint64_t)) It's interesting that on x86 we've got a longterm request to *add* cpu features to the stream to detect screwups caused by using mismatched CPUs; so it's not necessarily a bad idea to include it once you realise it's there. Dave > > > > -Aaron > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK