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 2CF2BC433EF for ; Mon, 31 Jan 2022 18:10:22 +0000 (UTC) Received: from localhost ([::1]:59302 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nEb88-0001Ms-CG for qemu-devel@archiver.kernel.org; Mon, 31 Jan 2022 13:10:20 -0500 Received: from eggs.gnu.org ([209.51.188.92]:36858) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nEb4x-0008Kl-1q for qemu-devel@nongnu.org; Mon, 31 Jan 2022 13:07:03 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:57550) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nEb4v-0000e2-5x for qemu-devel@nongnu.org; Mon, 31 Jan 2022 13:07:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643652420; 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=el1oz8JyGWZPg9SufF6Fo02PQVvaz9UNaDjL58T5h1I=; b=Y2anmtHeSgc718c9Sb52haHz9AH5Q7rJC6HCGt+EXmoyge257tKdFiTjeZwOjceniILZt3 VTxpxfpbPQvMhA4ax20dUI/hTyrXiFmkfmUkGya5yLM/QJjw3ejM34kCzWnkGGCOvbrPzP kTN99Q9j8Jz7BOCO0kM2DjsVNbW3ZT8= 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-180-ds_MB5qJMcGoM5PgynJaww-1; Mon, 31 Jan 2022 13:06:53 -0500 X-MC-Unique: ds_MB5qJMcGoM5PgynJaww-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9066885EE64; Mon, 31 Jan 2022 18:06:52 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.12]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 97B6C7DE23; Mon, 31 Jan 2022 18:06:51 +0000 (UTC) Date: Mon, 31 Jan 2022 18:06:48 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: David Edmondson Subject: Re: [RFC PATCH 1/1] i386: Remove features from Epyc-Milan cpu Message-ID: References: <20220129102336.387460-1-leobras@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline 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: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.088, 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, T_SCC_BODY_TEXT_LINE=-0.01 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?= Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jan 31, 2022 at 11:14:42AM +0000, David Edmondson wrote: > On Saturday, 2022-01-29 at 07:23:37 -03, Leonardo Bras wrote: > > > While trying to bring a VM with EPYC-Milan cpu on a host with > > EPYC-Milan cpu (EPYC 7313), the following warning can be seen: > > > > qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.erms [bit 9] > > qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EDX.fsrm [bit 4] > > > > Even with this warning, the host goes up. > > > > Then, grep'ing cpuid output on both guest and host, outputs: > > > > extended feature flags (7): > > enhanced REP MOVSB/STOSB = false > > fast short REP MOV = false > > (simple synth) = AMD EPYC (3rd Gen) (Milan B1) [Zen 3], 7nm > > brand = "AMD EPYC 7313 16-Core Processor " > > > > This means that for the same -cpu model (EPYC-Milan), the vcpu may or may > > not have the above feature bits set, which is usually not a good idea for > > live migration: > > Migrating from a host with these features to a host without them can > > be troublesome for the guest. > > > > Remove the "optional" features (erms, fsrm) from Epyc-Milan, in order to > > avoid possible after-migration guest issues. > > > > Signed-off-by: Leonardo Bras > > --- > > > > Does this make sense? Or maybe I am missing something here. > > We have encountered some Milan CPUs (7J13) that did not initially > declare support for either ERMS or FSRM. > > A firmware update caused these features to appear, which definitely > causes potential problems with migration of VMs from hosts with updated > firmware to those without. > > It would be interesting to know if there is any expectation that the > features might be enabled on the 7313 CPUs that you have with a future > firmware update. > > I *think* that the expectation is that Milan CPUs will have the > features, and if that is correct then they should remain present in the > EPYC-Milan definition on QEMU. Agreed, if this is just a case of outdated firmware, then I think it is a non-issue for our CPU model definition. Libvirt will ensure migration compatibility by launching the target QEMU with a -cpu arg that results in a model that matches the source QEMU exactly. It is merely a slight annoyance if someone launches a VM on a host with new firmware and tries to migrate to a host with old firmware. In that case though the answer is really to upgrade the firmware. > > Having a kvm guest running with a feature bit, while the host > > does not support it seems to cause a possible break the guest. > > As Daniel said, this should not happen in this case. > > > target/i386/cpu.c | 5 +---- > > 1 file changed, 1 insertion(+), 4 deletions(-) > > > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > > index aa9e636800..a4bbd38ed0 100644 > > --- a/target/i386/cpu.c > > +++ b/target/i386/cpu.c > > @@ -4160,12 +4160,9 @@ static const X86CPUDefinition builtin_x86_defs[] = { > > CPUID_7_0_EBX_FSGSBASE | CPUID_7_0_EBX_BMI1 | CPUID_7_0_EBX_AVX2 | > > CPUID_7_0_EBX_SMEP | CPUID_7_0_EBX_BMI2 | CPUID_7_0_EBX_RDSEED | > > CPUID_7_0_EBX_ADX | CPUID_7_0_EBX_SMAP | CPUID_7_0_EBX_CLFLUSHOPT | > > - CPUID_7_0_EBX_SHA_NI | CPUID_7_0_EBX_CLWB | CPUID_7_0_EBX_ERMS | > > - CPUID_7_0_EBX_INVPCID, > > + CPUID_7_0_EBX_SHA_NI | CPUID_7_0_EBX_CLWB | CPUID_7_0_EBX_INVPCID, > > .features[FEAT_7_0_ECX] = > > CPUID_7_0_ECX_UMIP | CPUID_7_0_ECX_RDPID | CPUID_7_0_ECX_PKU, > > - .features[FEAT_7_0_EDX] = > > - CPUID_7_0_EDX_FSRM, > > .features[FEAT_XSAVE] = > > CPUID_XSAVE_XSAVEOPT | CPUID_XSAVE_XSAVEC | > > CPUID_XSAVE_XGETBV1 | CPUID_XSAVE_XSAVES, > > dme. > -- > I don't care 'bout your other girls, just be good to me. > > 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 :|